Process for Producing Polyamide-Based Resin Film Roll

ABSTRACT

The present invention provides a process for production of a polyamide based resin film roll comprising a step of melt-extruding and cooling wherein polyamide based resin is melt-extruded and cooled in a sheet form onto a mobile cooling material surface to obtain an unstretched sheet; a step of biaxial stretching wherein an unstretched sheet is stretched biaxially in the longitudinal direction and the transverse direction; and a step of winding up the biaxially stretched film that is biaxially stretched in a form of roll. Then, in the step of melt-extruding and cooling polyamide based resin onto a mobile cooling material surface, corona discharge in a streamer corona state is performed between an electrode applied with high DC voltage and the polyamide based resin sheet in the melted state, and sufficient electric charges that enable the polyamide based resin sheet in the melted state to come in close contact with the mobile cooling material surface are imparted.

TECHNICAL FIELD

The present invention relates to a process for producing a film roll bytaking up a polyamide based resin film having high quality andhomogeneous mechanical properties over a long length, and specifically,to a process for producing a polyamide based resin film roll withexcellent workability in use of packaging such as retort food bylaminating with a polyolefin based resin film.

BACKGROUND ART

A biaxially oriented polyamide based resin film composed of nylon inmajor components is excellent in toughness, gas-barrier, pinholeresistance, transparency, printing property and the like, so that it iswidely utilized as a packaging material in various kinds of foods suchas a variety of liquid food, aqueous food, frozen food, retort food,paste food, cattle meat and aquatic food. Particularly in recent years,it is used extensively in packaging of retort food. Such polyamide basedresin film is laminated with polyolefin based resin films such aspolyethylene and polypropylene, folded in two parallel to its machinedirection, then thermally adhered in three sides and cut out to give abag with one side opened and three edges sealed in an opened state, inwhich various kinds of food etc. are filled and sealed, then sterilizedby heating in boiling water before being supplied to market.

In the case of using polyamide based resin film, however, there are someinstances that warpage occurs at corners of packaging bag after heatsterilization treatment to yield a curling phenomenon of four sides inS-shape (hereinafter called S-shaped curl phenomenon), resulting inremarkable deterioration of appearance as packaging goods. Therefore,regarding a method of reducing such curl phenomenon, as shown in Patentreference 1, there has been proposed a method to adjust a biaxiallyoriented polyamide based resin film to a specified value of product ofits boiling water shrinkage percentage and percentage change ofmolecular orientation angle in the direction of film width, but themethod needs an extremely high temperature in thermal fixation or excessthermal relaxation after stretching to enhance dimensional stability inboiling water treatment, thus it poses problems that the toughness andpinhole resistance of the resultant film are deteriorated.

Therefore, the present inventors have devised and proposed a method forobtaining a biaxially oriented polyamide based resin film free fromS-shaped curl phenomenon without lowering toughness and pinholeresistance by adjusting boiling water shrinkage percentage andrefraction index of film within a specified numeric range as describedin Patent reference 2.

Patent reference 1: Japanese Unexamined Patent Publication Hei 4-103335(1992)Patent reference 2: Japanese Unexamined Patent Publication Hei 8-174663(1996)

DISCLOSURE OF THE INVENTION Problems to be solved by the Invention

According to the method of Patent reference 2 described above, itbecomes possible to obtain a biaxially oriented polyamide based resinfilm free from S-shaped curl phenomenon having excellent toughness andpinhole resistance. However, in a bag forming processing by lamination,since conditions of pressure and time in thermal adhesion are finelyadjusted for every film roll used, even in the case where the averagevalues of boiling water shrinkage percentage and refraction index of thefilm wound up in a film roll are in the range of Patent reference 2,when degree of variation in one film roll is large, wrinkle takes placebetween films each other on lamination in a bag forming processing,which tends to pose troubles such as bad yield ratio.

On the other hand, the present inventors have proposed, in a productionmethod of biaxially stretched film roll by winding up a biaxiallystretched film after melt extrusion of a plurality of resins mixed, as amethod to reduce variation of coefficient of dynamic friction, a methodto reduce segregation of feedstock by homogenizing the shape offeedstock chip or enlarging the angle of slope of a funnel-shaped hopperas a feed section of feedstock into an extruder (Japanese UnexaminedPatent Publication 2004-181777). However, the method also cannotnecessarily be conclusive for a method to suppress the variation andfluctuation of mechanical properties such as boiling water shrinkagepercentage and refraction index of film wound in a film roll.

As a result of committed research on production techniques to produce abiaxially stretched film roll with high homogeneity, the presentinventors invented a polyamide based resin film roll with highhomogeneity in film thickness, boiling water shrinkage percentage andrefraction index, and other physical properties and capable of bagforming processing smoothly with good yield ratio free of wrinklesbetween films efficiently at lamination (Japanese Unexamined PatentPublication 2004-262922).

In producing the above-mentioned polyamide based resin film roll, asheet melt-extruded through dies from an extruder is cooled andsolidified on mobile cooling material such as cooling rolls (metalrolls), etc. to form an unstretched sheet. In cooling and solidificationby such cooling rolls, bringing the polyamide based resin sheet in amelted state directly in close contact with the mobile cooling materialwithout intervention of a thin air layer enables rapid cooling of meltedresin and enables the production of an unstretched sheet of low degreeof cristallinity. Consequently, in cooling and solidification by coolingrolls, in order to forcibly bring the extruded melted sheet in closecontact with the cooling material surface in a short time, there adoptedis a method to install a wire-form electrode between the dies and themobile cooling material to deposit static loads on the surface of theunsolidified sheet and to forcibly bring the unsolidified sheet in closecontact with the cooling material surface (hereinafter the moldingmethod of unsolidified sheet by the use of forcible close contact bystatic charges is referred to as the static electricity applied moldingmethod).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

However, in the case of slow sheet take-up speed, close contact bystatic charges separated out on the sheet surface is enabled, but whenthe take-up speed is increased, close contact by static electricitybecomes disabled, and a thin air layer enters between the sheet in themelted state and the mobile cooling material surface, variations insheet thickness increases, cooling of melted sheet is delayed, coolingirregularity occurs, and a sheet with advanced crystallization and atthe same time with defective transparency containing crystallizationirregularities is obtained. Furthermore, oligomers of polyamide basedpolymers separated out on the mobile cooling material surface.Consequently, increasing voltage applied to electrode disposed betweenthe dies and the mobile cooling material surface in order to increasethe electrostatic load amount to be precipitated on the sheet-formsubstance surface generates noncontinuous arc discharge between theelectrode and the cooling material surface, destroys the sheet-formsubstance on the cooling material surface, and in an extreme case,destroys the surface coating of the cooling material. Consequently, thevoltage applied to the electrode is unable to be increased to becomehigher than a certain level, and in the conventional static electricityapplication method, it was unable to produce highly homogeneouspolyamide based resin film roll with sufficiently increasing the filmforming speed as is the case with the Japanese Unexamined PatentPublication 2004-262922.

The present invention has been achieved by the present inventors as aresult of committed research and development on conventional productiontechniques to successfully impart high electric current at low voltagewithout any arc discharge by using a multi-needle form electrode,carrying out corona discharge in a stream corona state between themulti-needle form electrode and a melted resin sheet, and impartingsufficient electric charges to bring the mobile cooling material surfacein close contact with the polyamide based resin sheet in a melted statewhen film-formable polyamide based resin is melt-extruded and cooled onthe mobile cooling body surface. Then, the present inventors of thepresent invention found that by this, various defects in theconventional static electricity-applied molding method can be solved ata stroke and polyamide based resin sheet which does not cause oligomersto accumulate on the mobile cooling material and provides superbthickness uniformity and transparency and low degree of cristallinity,as well as little crystallization irregularities can be formed into filmat a high speed and in forming film at a regular speed (conventionalspeed), still more stable film formability can be achieved, and reachedthe present invention.

Means to Solve the Problems

The present inventions, the constituent of the invention described inclaim 1 is a process for producing a polyamide based resin film rollwound up in a width of 0.2 m (m is meter) or more, 3.0 m or less, and alength of 300 m or more, 30000 m or less, comprising: a step ofmelt-extruding and cooling wherein polyamide based resin ismelt-extruded and cooled in a sheet form onto a mobile cooling materialsurface to obtain an unstretched sheet; a step of biaxial stretchingwherein an unstretched sheet is stretched biaxially in the longitudinaldirection and the transverse direction; and a step of winding up thebiaxially stretched film that is biaxially stretched in a form of roll,and the step of melt-extruding and cooling performs corona discharge ina streamer corona state between an electrode applied with high dcvoltage and the polyamide based resin sheet in the melted state, andimparts sufficient electric charges that enable the polyamide basedresin sheet in the melted state to come in close contact with the mobilecooling material surface, and satisfies the following requirements (1)and (2) as well as the following requirements (3), when the polyamidebased resin film wound up in a form of a roll has a first sample cutoutportion set up within 2 m from the winding end of film and a finalcutout portion within 2 m from the winding start of film, and at thesame time has a sample cutout portion set up at approximately every 100m from the first sample cutout portion;

(1) when a maximum boiling water shrinkage percentage which is themaximum value of boiling water shrinkage percentages in all directions,of each sample cut out from each of the cutout portions is measured, themaximum boiling water shrinkage percentage, an average boiling watershrinkage percentage which is average value of the maximum boiling watershrinkage percentages is 2% to 6%, and a degree of variability in themaximum boiling water shrinkage percentages of all samples is within arange of ±2% to ±10% relative to the average boiling water shrinkagepercentage;(2) when a directional difference of boiling water shrinkage percentagewhich is an absolute value of the difference between a boiling watershrinkage percentage in the direction of +45° to the longitudinaldirection and a boiling water shrinkage percentage in the direction of−45° to the longitudinal direction of each sample cut out from each ofthe cutout portion is determined, an average directional difference ofboiling water shrinkage percentage which is the average of thedirectional differences of boiling water shrinkage percentage is 1.5% orless, and a degree of variability in the directional differences ofboiling water shrinkage percentage of all samples is within a range of±2% to ±10% relative to the average directional difference of boilingwater shrinkage percentage; and(3) a degree of variability in the thickness of a roll wound up over theentire length in the longitudinal direction is within ±2% to ±10%relative to the average thickness.

The constituent of the invention described in claim 2 is, in theinvention described in any of claim 1, the roll wherein when refractionindex in the thick direction of each sample cut out from each of thecutout portions is measured, an average refraction index which is theaverage value of the refraction indexes is 1.500 or more, 1.520 or less,and a degree of variability in the refraction indexes of all samples iswithin a range of ±2% relative to the average refraction index.

The constituent of the invention described in claim 3 is, in theinvention described in claim 1, the roll wherein when refraction indexin the thick direction of each sample cut out from each of the cutoutportions is measured, an average refraction index which is the averageof the refraction indexes is 1.500 or more, 1.520 or less, and a degreeof variability in the refraction indexes of all samples is within arange of ±1% relative to the average refraction index.

The constituent of the invention described in claim 4 is, in theinvention described in claim 1, the roll wherein the major component ofpolyamide composing the polyamide based resin film is nylon 6.

The constituent of the invention described in claim 5 is, in theinvention described in claim 1, the roll wherein polyamide based resinfilm formed from a mixture of two or more different types of mixedsubstances of polyamide based resin is wound up.

The constituent of the invention described in claim 6 is, in theinvention described in claim 1, the roll wherein the polyamide basedresin film wound up is laminated with a polyolefin based resin film.

The constituent of the invention described in claim 7 is, in theinvention described in claim 1, the roll which is a polyamide basedresin film taken up being stretched by a tenter stretching method.

The constituent of the invention described in claim 8 is, in theinvention described in claim 1, the roll which is a polyamide basedresin film taken up being sequentially biaxially stretched.

The constituent of the invention described in claim 9 is, in theinvention described in claim 1, the roll which is a polyamide basedresin film taken up wherein an substantially unoriented sheet-likesubstance of polyamide based resin is stretched in at least two stagesin the longitudinal direction to be threefold or more at a highertemperature than the glass transition temperature of the polyamide basedresin +20° C., then stretched in the transverse direction to bethreefold or more.

The constituent of the invention described in claim 10 is, in theinvention described in claim 1, the roll which is a polyamide basedresin film taken up being thermally fixed after a final stretchingtreatment.

The constituent of the invention described in claim 11 is, in theinvention described in claim 1, the roll which is a polyamide basedresin film taken up being thermally fixed after releasing treatment.

The constituent of the invention described in claim 12 is, in theinvention described in claim 1, the roll wherein at least one kindselected from lubricant, anti-blocking agent, thermal stabilizer,antioxidant, antistatic agent, light resistant agent and impact modifieris added into the polyamide based resin film wound up.

The constituent of the invention described in claim 13 is, in theinvention described in claim 1, the roll wherein inorganic particle isadded into the polyamide based resin film wound up.

The constituent of the invention described in claim 14 is, in theinvention described in claim 13, the roll wherein the inorganic particleis a silica particle of 0.5-5.0 μm in an average diameter.

The constituent of the invention described in claim 15 is, in theinvention described in claim 1, the roll wherein a higher fatty acid isadded into the polyamide based resin film wound up.

The constituent of the invention described in claim 16 is, in theinvention described in claim 1, the roll wherein corona discharge in astream corona state in the melt-extrusion and cooling step takes placebetween a multi-needle-form electrode to which dc high voltage isapplied and the polyamide based resin sheet in a melted state.

EFFECT OF THE INVENTION

According to the production process of the present invention, polyamidebased resin sheet with uniform thickness, low degree of crystallinity,superb transparency, and further little crystallization irregularitiescan be formed into film at a high speed, and contamination of the mobilecooling material by oligomers is not generated. Consequently, accordingto the production process of the present invention, a highly uniformpolyamide based resin film roll can be manufactured extremelyefficiently with the film forming speed sufficiently increased as is thecase with the Japanese Unexamined Patent Publication 2004-262922. Thatis, using the polyamide based resin film roll obtained by the productionprocess of the present invention at a high productivity, bag formingprocessing can be conducted smoothly by lamination with almost notroubles to give a package free from S-shaped curl efficiently. Also, itbecomes possible to obtain processed goods with high yield ratio in apost treatment like bag forming processing. In addition, in use of thepolyamide based resin film roll obtained by the production process ofthe present invention, a bag for food packaging after bag formingprocessing becomes excellent in toughness and pinhole resistance.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferable aspect of production method for obtaining a polyamide basedresin film roll of the present invention will be described as follows.According to the production process of the present invention, thepolyamide based resin film roll of the present invention is produced asfollows: an unstretched film obtained by melt-extrusion of Polyamidebased resin (polyamide resin chip raw material) is stretched biaxially(in the longitudinal direction) and transverse direction (widthdirection) and wound up in a form of roll.

As a polyamide resin used in the present invention, for example, therecan be listed nylon 6 of ε-caprolactam as a major raw material. Also, asother polyamide resins, there can be listed a polyamide resin obtainedby polycondensation of lactam with three-membered ring or more, ω-aminoacid, dicarboxylic acid and diamine. Specifically, lactams includeenantlactam, capryllactam, lauryllactam other than ε-caprolactamabove-mentioned; ω-amino acids include 6-aminocaproic acid,7-aminoheptanoic acid, 9-aminononanoic and 11-aminoundecanoic acid.Also, dicarboxylic acids include adipic acid, glutaric acid, pimelicacid, suberic acid, azelaic acid, sebacic acid, undecanedione acid,dodecadione acid, hexadecadione acid, eicosandione acid,eicosadienedione acid, 2,2,4-trimethyladipic acid, terephtahlic acid,isophthalic acid, 2,6-naphtahalene dicarboxylic acid, andxylylenedicarboxylic acid. Further, diamines include ethylenediamine,trimethylenediamine, tetramethylenediamine, hexamethylenediamine,pentamethylenediamine, undecamethylenediamine, 2,2,4 (or,2,4,4)-trimethylhexamethylenediamine, cyclohexanediamine,bis-(4,4′-aminocyclohexyl)methane, and methaxylylenediamine. Polymersobtained by polycondensation of these chemicals and copolymers thereof,for example, nylons 6, 7, 11, 12, 6.6, 6.9, 6.11, 6.12, 6T, 6I, MXD6(methaxyleneadipamide 6), 6/6.6, 6/12, 6/6T, 6/6I, 6/MXD6 can be used.In addition, in the case of producing polyamide film roll of the presentinvention, the above polyamide resin can be used alone or in a mixtureof 2 kinds or more thereof.

Additionally, of the above polyamide based resins, particularlypreferable resin in the present invention has relative viscosity in arange of 2.0 to 3.5. The relative viscosity of polyamide based resinaffects toughness of biaxially stretched film obtained and stretchingproperty. That is, when relative viscosity is less than 2.0, impactstrength becomes somewhat insufficient, whereas when relative viscosityis more than 3.5, sequentially biaxially stretching property tends to bebad because of increase in stretching stress. Additionally, the relativeviscosity in the present invention means a value that a solution of 0.5g of polymer dissolved in 50 ml of 97.5% sulfuric acid is measured at25° C.

In melt-extrusion of the polyamide based resin (polyamide based resinchip raw material), extrusion is carried out by a flat plate by flatdies such as T dies and I dies. The extruded sheet is cooled on thesurface of the mobile cooling material such as cooling rolls (metalrolls), etc. and is obtained as a practically unoriented sheet. In orderto suppress crystallization of the extruded sheet, the coolingtemperature of the extruded sheet is preferably between the temperaturerange of the dew point or higher and the maximum crystallizationtemperature of −20° C. or lower. In the foregoing description, themaximum crystallization temperature (Tc) is determined by DSC(differential scanning calorimeter), and is generally between 180 and200° C. in the case of nylon 6, but is varied by the types of polymersand addition of various additives. When the cooling temperature of theextruded sheet is Tg +10° C. or higher, the cooled sheet is likely to bedeformed, and it is preferable to further carry out the second-stepcooling in order to cool at Tg+10° C. or lower. For cooling the extrudedsheet, a cooling means by applying the cooling fluid from the sideopposite to the mobile cooling material surface, spraying cooling gas,immersion in a cooling liquid tank, etc. can be combined.

The surface of the mobile cooling material may be either mirror-finishedor rough-surface finished. For the surface material, the material thatcan stand long-term use is preferable but is not particularly limited.Hard chromium plating, ceramic coating, Teflon (registered trademark)coating, etc. can be illustrated as surface material.

The high-voltage direct current used in the present invention may havesome ac components overlapped, but it is preferable to use a dc powersupply with the voltage or current stabilized as much as possible, andit is more preferable to use a dc power supply whose ripple (peak topeak) is 1.0 or less % when a dummy resistor is connected across theoutput terminal and the grounding terminal, and the voltage or currentis measured. The polarity of the electrode is not limited, but thenegative potential is particularly preferable.

The feature of the present invention lies in generating corona dischargein the streamer corona state between the electrode and the melt-extrudedpolyamide based resin sheet to impart a high electric current at lowvoltage, and can impart the current more than tens of times as much asin the static electricity applied molding method. Now, the coronadischarge in the streamer corona state means a stable corona conditionwith the electrode and grounding flat plate (melted resin sheet) bridged(see Japanese Examined Patent Publication No. Sho 62-41095). In theevent that the electrode is of positive electric potential, a coronaconcentrated in a form of a rod is formed from the electrode head end tothe melted sheet, while in the case of negative electric potential, acorona expanded in a form of a hanging temple bell is formed from theelectrode head end to the melted sheet, but for the corona electricdischarge in the streamer corona state in the present invention, eitherstates of corona discharge can be adopted.

In order to stably generate corona discharge in the streamer coronastate of the present invention, the discharge points must be disposed innoncontinously. To achieve this, for example, multi-needle-formelectrodes (electrodes with a large number of needle-form materialsplaced side by side nearly free of any clearance in the same directionfrom a long-size support material covered with insulator such assilicon, etc.) or serrate electrodes are preferable, but in the presentinvention, it is not particularly limited to these. The number andarrangement method of discharge points may be optionally selected. Inaddition, the material of discharger may be anything if it iselectrically conductive, and the example can include metal(particularly, stainless steel), carbon, etc. By the way, theneedle-form material at the multi-needle form electrodes preferably hasa sharp-angled head end. Furthermore, in the event that the head end ofthe needle-form material is sharp-angled, the thickness of the portionother than the head end is preferably between 0.5 and 5.0 mm (indiameter) because the streamer corona discharge state becomes still morestable, and is more preferably between 1.0 and 3.0 mm in diameter. Inaddition, it is not necessary to discharge electricity from all theneedle-shape materials of the multi-needle electrode to the melted resinsheet but intervals of stream corona discharge may be suitably changedby adjustment or the like of the applied voltage.

Furthermore, in order to stably generate corona discharges in thestreamer corona state in the method of the present invention, forexample, the clearance between the electrode discharge point and themelted resin sheet is preferably between 2 and 20 mm, and particularlypreferably between 2 and 10 mm. By arranging the discharging points inthis way, stable stream corona discharge accompanied by the luster isgenerated between the electrode and the polyamide based resin sheet in amelted state and at the same time, high electric current flows.Furthermore, the thickness of the sheet formed by the present inventionis not particularly limited but is preferably between 50 and 500 μm, andmore suitably between 100 and 300 μm. On the other hand, the take-upspeed of the sheet formed by the present invention is not particularlylimited, either. The maximum take-up possible speed by the conventionalstatic electricity applied molding method is about 50 m/min, but in themethod of the present invention, it is possible to cool in close contacteven at 80 m/min, which exceeds this take-up speed. By the way, in theevent that streamer corona discharge is utilized as described above, themaximum take-up possible speed can be remarkably increased but whenstreamer corona discharge is utilized at the normal take-up speed, thestill more stable film formability can be achieved, and breakagefrequency can be markedly reduced.

In addition, when streamer corona discharge is performed as describedabove, adjusting the voltage to be applied to a range of 7 to 14 kv canreduce thickness irregularities in the longitudinal direction of thefilm roll, fluctuations and variations of physical properties, which ispreferable. In addition, in the process for producing film rollaccording to the present invention, variations of voltage to be appliedmust be suppressed within the average voltage (set value) ±20%, and morepreferably within ±10%.

Furthermore, in the event that streamer corona discharge is performed asdescribed above, adjusting the atmosphere around the electrode, humidityto 40-85% RH, and temperature to a range of 35 to 55° C. in such amanner as to prevent the sheet from being in a dry state and make in aslightly more moistened state and as to prevent the dew point from beingformed, the condition in which oligomers (oligomers of ε-caprolactam,etc.) adhere to the needle tip end or serrate tip end can be prevented,and the stable streamer corona discharge can be achieved, which ispreferable. By the way, the range of still more preferable humidity isbetween 60 and 80% RH and the range of still more preferable temperatureis between 40 and 50° C.

Next, referring to a drawing, the process according to the presentinvention will be described. FIG. 1 is an explanatory diagram showingone embodiment of a process for producing sheets according to theprocess of the present invention. In FIG. 1, sheet form melted material2 is extruded from a die 1, and is cooled and solidified by a coolingdrum 3 to be formed into an unstretched sheet 4. By a dc high voltagesupply 5, voltage is applied to the electrode 6 and streamer coronadischarge 7 is generated in the sheet form melted material by theelectrode 6.

According to the process for producing the present invention, thepolyamide based resin film roll is produced by biaxially stretching anunstretched sheet obtained by melt-extrusion and cooling of resin(polyamide resin chip) in the longitudinal direction (length direction)and transverse direction (width direction) and then by winding it upinto a roll.

The present inventors have studied on thickness irregularity of filmroll in the longitudinal direction (thickness irregularity over theentire length of film roll), and variation and fluctuation of physicalproperties like boiling water shrinkage percentage, as a result, it hasbeen found that the thickness irregularity in the longitudinaldirection, and variation and fluctuation of the physical properties arelargely influenced by various factors mainly in a casting step of meltedresin into an unstretched film. Namely when a resin fed into afunnel-shaped hopper (hereinafter simply called hopper) connecteddirectly with an extruder has a low temperature, or a resin fed into ahopper has a high water content, thickness irregularity of theunstretched film in the longitudinal direction becomes large, andvariation and fluctuation of the physical properties of the biaxiallystretched film become large. It has been also found that thicknessirregularity of the unstretched film in the longitudinal directionbecomes large and variation and fluctuation of the physical propertiesof the biaxially stretched film become large when contact point betweenthe resin and a metal roll is in turbulence in winding resin extrudedfrom a T-die on the metal roll. Further, it has been found that whenstretching conditions are not suitable in a step of biaxial stretching,thickness irregularity of the unstretched film in the longitudinaldirection is amplified, increasing variation and fluctuation of thephysical properties.

Further, the present inventors have keenly studied on the basis of theforegoing facts. As a result, they learned that in producing a filmroll, a film roll with less variation of physical properties can beobtained by the following measures:

(1) uniformity of shape of resin chip(2) suitable shape of hopper(3) reduction of water content in drying resin chip(4) retention of temperature in feeding resin to hopper(5) suction for contacting melted resin with metal roll(6) suitable stretching condition Each of the above measures will besequentially described below.

(1) Uniformity of Shape of Resin Chip

In the production of film roll of the present invention, in the case ofadopting a blend method, a plurality of polyamide resin chips of rawmaterials different in composition are blended in a hopper, then meltblended and extruded from an extruder to form a film. For example, inthe case of three kinds of polyamides as feedstock, respective polyamideresin chips are fed into respective three hoppers continuously orintermittently, via a buffer hopper if necessary, and finally whilethree kinds of polyamide resin chips are being mixed in a hopper justbefore or just above an extruder (hereinafter called final hopper),feedstock chips are quantitatively fed into the extruder in accordancewith the extrusion rate of extruder to form a film.

However, depending on a capacity or shape of final hopper, when theamount of chip in the final hopper is large or when the amount of chipin the final hopper becomes small, there occurs a phenomenon offeedstock segregation, namely, a phenomenon in which chip compositionfed to an extruder from the final hopper becomes uneven. Also, suchsegregation phenomenon appears remarkably, in particular when chip shapeor specific gravity is different. Further, resulting from suchsegregation phenomenon, in the case of producing a long film, thereoccur the variations of maximum boiling water shrinkage, directionaldifference of boiling water shrinkage, film thickness and refractionindex in the thickness direction.

Namely, in the presence of different chip sizes, when a mixture of chipsfalls in a final hopper, smaller chip is apt to fall first, when theremaining amount of chip in the final hopper becomes small, the ratio oflarger chip becomes more, which causes the chip segregation. Therefore,in order to obtain a film with less variation of physical properties, itis necessary to uniform the shape of polyamide resin chip with aplurality of kinds being used to suppress a phenomenon of feedstocksegregation in the final hopper.

Feedstock chip of polyamide is generally formed by being drawn off in astrand of melted state from polymerization equipment afterpolymerization, immediately water-cooled, and then cut by a strandcutter. Thus, polyamide chip is of elliptic cylinder with elliptic crosssection. As the result of studies on the relationship between shape ofpolymer chip and feedstock segregation, an average major axis (mm),average minor axis (mm) of elliptic cross section and average chiplength (mm) of polyamide chip mixed other than a polyamide chip with thelargest amount used is adjusted each within a range of ±20% relative tothe average major axis (mm), average minor axis (mm) of elliptic crosssection and average chip length (mm) of the polyamide chip with thelargest amount used, thereby it becomes possible to reduce theabove-mentioned feedstock segregation. Additionally, it is morepreferable, to result in a remarkable segregation preventing effect,that an average major axis, average minor axis of elliptic cross sectionand average chip length of polyamide chip mixed other than a polyamidechip with the largest amount used is adjusted each within a range of±15% relative to the average major axis, average minor axis of ellipticcross section and average chip length of the polyamide chip with thelargest amount used.

(2) Suitable Shape of Hopper

It is effective for reducing feedstock segregation that using afunnel-shaped hopper as a final hopper whose angle of slope is set to65° or more, thereby large chip can fall easily in the same manner assmall chip, and the upper part of contents goes down while keeping itshorizontal plane. More preferable angle of slope is 70° or more.Additionally, angle of slope of hopper means an angle between obliqueline of hopper and horizontal line segment. A plurality of hoppers maybe used in the upstream of final hopper, in this case, any hopper musthave an angle of slope of 65° or more, 70° or more is more preferable.

Also, reducing the ratio of fine powder formed due to shaving feedstockchip used is preferable to suppress the variation of boiling watershrinkage percentage. Since the fine powder advances feedstocksegregation, it is preferable to eliminate fine powder formed in processto reduce the ratio of fine powder contained in a hopper. The ratio offine powder contained is preferably within 1% by weight through theentire steps before feedstock chip enters into an extruder, morepreferably within 0.5% by weight. As a specific method for reducing theratio of fine powder, there can be listed a method of sieving in chipforming step by a strand cutter or passing through a cyclone type airfilter in transporting feedstock chip with air.

In addition, as a means for reducing feedstock segregation in a hopper,setting a suitable capacity of hopper used is also a preferable means.Here, the suitable capacity of hopper is in a range of 15-120% by weightrelative to the extrusion amount per one hour of extruder, morepreferable is in a range of 20-100% by weight relative to the extrusionamount per one hour of extruder.

As a method for blending feedstock chips of polyamide having two or morekinds different in composition, the most preferable method is to blendin a hopper (final hopper) just above an extruder while quantitativelyfeeding each feedstock into the extruder continuously. Also, it ispossible to feed into a final hopper and extruder via severalintermediate hoppers (buffer hoppers) after premixing feedstock chipwhose size is controlled within the range described above. In blending aplurality of feedstock, there can be listed a method of blending whilefeeding a plurality of feedstock quantitatively into a hopper from anapparatus quantitatively feeding feedstock chip continuously, or amethod of blending beforehand using a blender or a paddle drier, in thecase of adopting the latter, it is preferable to make the size offeedstock chip small not to generate feedstock segregation indischarging a mixture.

(3) Reduction of Water Content in Drying Resin Chip

Chip fed into a hopper is generally heated by a machine like blender toreduce moisture therein. In drying the chip, it has been thought thatthe lower content in drying in production of polyester film roll orpolypropylene film roll generally yields the better film roll due tosuppression of hydrolysis in an extrusion step. However, the followingfact has been found from the result of the studies by the presentinventors: in production of polyamide based resin film roll, a merereduction of water content in drying makes stretching difficult to yieldno film roll of homogenous physical properties, but the water content iscontrolled within a given range to reserve some level of moisture, whichleads to a suitable plasticization without being hydrolyzed in anextrusion step to thereby give a film roll with homogenous physicalproperties. Namely, to obtain the film roll of the present invention, itis necessary to control the water content of chip in 800 ppm or more,and 1000 ppm or less. When the water content of chip exceeds 1000 ppm,hydrolysis is advanced when melted, which lowers viscosity. Therefore,thickness irregularity of unstretched film in the longitudinal directionbecomes bad and the thickness irregularity of biaxially stretched filmin the longitudinal direction is increased, which causes the variationand fluctuation of physical properties. On the other hand, when thewater content of chip is less than 800 ppm, viscosity when meltedbecomes too high, which deteriorates film forming property (ease ofstretching). Additionally, most suitable water content of chip fed to ahopper is 850 ppm or more, and 950 ppm or less.

(4) Retention of Temperature in Feeding Resin to Hopper

As described above, even in the case of adjusting water content of chipto 800 ppm or more, and 1000 ppm or less, a film roll with homogenousphysical properties cannot be obtained when chip after heat-drying beingallowed to stand down to ambient (room) temperature is fed into ahopper. Namely, to obtain a film roll of the present invention, it isnecessary to feed into a hopper while keeping the chip heat-dried by ablender etc. in high temperature. Specifically, it is necessary to feedinto a hopper while keeping the chip heat-dried by a blender at 80° C.or more, it is more preferably to feed into a hopper while keeping at90° C. or more. When the temperature of chip fed to a hopper is below80° C., resin charging becomes bad. This causes thickness irregularityin the longitudinal direction, and variation and fluctuation of physicalproperties, which produces no film roll of the present invention.Additionally, in drying chip by a blender etc., drying temperature isrequired at 15.0° C. or less. When the drying temperature is above 150°C., it is not preferable because hydrolysis may occur in drying. Also,when the temperature of chip heat-dried by a blender is below 80° C., itis necessary to reheat the chip so as to be 80° C. or more beforefeeding it into a hopper.

(5) Suction for Contacting Melted Resin with Metal Roll

In obtaining an unstretched film by melt extrusion of chip, chip ismelted by an extruder at 200-300° C., and extruded through a T-die toform a film (sheet), i.e., by casting, then quenched by a method ofwinding on a cooling roll such as metal roll being cooled at a giventemperature. Additionally, from the points of thickness irregularity inthe longitudinal direction, and variation and fluctuation of physicalproperties, preferable temperature of melt extrusion is 240° C. to 290°C. To obtain a film roll of the present invention, in the case ofwinding melted resin on a metal roll, it is preferable to force themelted resin to contact a metal roll by the following manner: air gap(namely, a distance between the exit of T-die lip and a surface ofchilling roll in the vertical direction) is adjusted to 20-60 mm, andthe part contacting the melted resin with the surface of cooling roll issucked over the entire width of melted resin in the opposite directionto the winding direction by utilizing a suction unit such as vacuum box(vacuum chamber) having a wide suction inlet. Also, in this case, windvelocity of suction air in the suction inlet must be adjusted to 2.0-7.0m/sec., and it is more preferably adjusted to 2.5-5.5 m/sec. Further,vacuum box may have a single suction inlet, and it is preferable thatthe suction inlet divided into a predetermined number of sections in thelateral direction can adjust the wind velocity of suction in eachsection to make the adjustment of wind velocity of suction easy in thesuction inlet. Also, when the casting speed increases, accompanyingstream takes place according to the rotation of metal roll, whichdisturbs close contact of melted resin with a metal roll, thus to makesuction more effective by a suction unit, and to improve close contactof melted resin with the metal roll, it is preferable to shield theaccompanying stream by equipping a masking shield of flexible materiallike Teflon being formed in broad range in the upstream adjacent to thesuction unit (the opposite side to the rotation direction of metal rollrelative to the suction unit). Further, to obtain a film roll of thepresent invention, fluctuation of wind velocity of suction (set value)in a vacuum box is required to be suppressed within ±20% to the averagewind velocity of suction, more preferably suppressed within ±10%. Inaddition, to prevent wind velocity of suction in a vacuum box fromvariation due to oligomer dust etc., it is preferable to control suctionpower by equipping a filter in a vacuum box and feed back thedifferential pressure across the filter.

(6) Suitable Stretching Condition

As a method of biaxially stretching an unstretched film, it is necessaryto adopt a longitudinal and transverse stretching method that anunstretched film is stretched by a roll-type stretching machine in thelongitudinal direction, stretched by a tenter-type stretching machine inthe transverse direction, then thermally fixed and relaxed. Further, toobtain a film roll by the production method of the present invention, asa method of biaxial stretching, it needs to adopt so calledlongitudinal-longitudinal-transverse stretching method. Such thelongitudinal-longitudinal-transverse stretching method is the followingmethod: in longitudinal-stretching of an essentially unorientedpolyamide film, the first-stage stretching is conducted, without coolingat Tg or less, and continuously the second-stage stretching isconducted, and then transverse stretching is conducted in a ratio of 3.0times or more, preferable 3.5 times or more, and further thermallyfixed. Moreover, to obtain a film roll of the present invention, inconducting the longitudinal-longitudinal-transverse stretching describedabove, a longitudinal stretching ratio in the first stage must be higherthan a longitudinal stretching ratio in the second stage. Namely, bysetting a longitudinal stretching ratio in the first stage higher than alongitudinal stretching ratio in the second stage, it becomes possibleto obtain a film roll having excellent physical properties such asboiling water shrinkage percentage and less fluctuation of thesephysical properties. Additionally, in the case of conducting thelongitudinal-longitudinal-transverse stretching, generally, when alongitudinal stretching ratio in the first stage is lower than alongitudinal stretching ratio in the second stage, stretching is easilycarried out without adhesion on a roll in the first stage. On the otherhand, even when a longitudinal stretching ratio in the first stage ishigher than a longitudinal stretching ratio in the second stage,stretching can be easily carried out without adhesion on a roll by usinga special roll such as roll made of Teflon (registered trademark).

In the case of conducting the longitudinal-longitudinal-transversestretching described above, it is preferable that a longitudinalstretching in the first stage is carried out in a temperature of 80-90°C. and a ratio of about 2.0-2.4 times. It is not preferable that thestretching ratio in the first stage is high beyond the foregoing rangebecause thickness irregularity in the longitudinal direction becomeslarge. In addition thereto, it is preferable that a longitudinalstretching in the second stage is carried out in a temperature of 65-75°C. and a ratio of about 1.3-1.7 times. It is not preferable that thestretching ratio in the second stage is low beyond the foregoing rangebecause distortion in boiling is too large to have a practical use.Reversely, it is not preferable that the stretching ratio in the secondstage is high beyond the foregoing range because strength (strength at5% extension) in the longitudinal direction is too low to have apractical use.

Also, in the case of conducting the longitudinal-longitudinal-transversestretching described above, a longitudinal stretching method can employa heated roll stretching or an infrared radiation stretching. Also, inthe case where a polyamide based resin film is produced by suchlongitudinal-longitudinal-transverse stretching method, it is possibleto reduce not only thickness irregularity, the variation and fluctuationof physical properties in the longitudinal direction but also thevariation and fluctuation of physical properties in the transversedirection. Also, in the case of conducting thelongitudinal-longitudinal-transverse stretching, the total longitudinalstretching condition is preferably 3.0 to 4.5 times.

Also, in the case of conducting the longitudinal-longitudinal-transversestretching, it is preferable that transverse stretching is carried outin a temperature of 120-140° C. and a ratio of about 4.0-5.5 times. Itis not preferable that the transverse stretching ratio is low beyond theforegoing range because strength (strength at 5% extension) in thetransverse direction is too low to have a practical use, reversely, itis not preferable that the transverse stretching ratio is high beyondthe foregoing range because thermal shrinkage in the transversedirection becomes high. Moreover, it is not preferable that temperaturein transverse stretching is low beyond the foregoing range becausedistortion in boiling is too large to have a practical use, reversely,it is not preferable that temperature in transverse stretching is highbeyond the foregoing range because strength (strength at 5% extension)in the transverse direction is too low to have a practical use.

Further, to obtain a film roll of the present invention, thermalfixation treatment after the longitudinal-longitudinal-transversestretching is preferably conducted in a temperature of 180-230° C. Whenthe temperature in the thermal fixation treatment is low beyond theforegoing range, it is not preferable because thermal shrinkage in thelongitudinal direction and transverse direction is large, and reversely,when the temperature in the thermal fixation treatment is high beyondthe foregoing range, it is not preferable because impact strength ofbiaxially stretched film becomes low.

In addition, to obtain a film roll of the present invention, relaxationtreatment after thermal fixation is preferably carried out in arelaxation of 2-10%. When the relaxation treatment ratio is low beyondthe foregoing range, it is not preferable because thermal shrinkage inthe longitudinal direction and transverse direction becomes large, andreversely, when the relaxation treatment ratio is high beyond theforegoing range, it is not preferable because strength (strength at 5%extension) in the longitudinal direction and the width direction is toolow to have a practical use.

Also, width of film roll is not particularly limited, but the lowerlimit of width of film roll is preferably 0.35 m or more from the pointof easy handling, more preferably 0.50 m or more. On the other hand, theupper limit of width of film roll is preferably 2.5 m or less, morepreferably 2.0 m or less, and further preferably 1.5 m or less. Inaddition, winding length is also not particularly limited, but the lowerlimit of width of film roll is preferably 500 m or more from the pointsof easy winding and easy handling, more preferably 1000 m or more. Onthe other hand, the upper limit of winding length of film roll ispreferably 25000 m or less, more preferably 20000 m or less, and furtherpreferably 15000 m or less. Additionally, in the case of film thicknessof about 15 μm, 12000 m or less is particularly preferable. Also,winding core can ordinarily employ a paper, plastic or metal core with 3inches, 6 inches, 8 inches and the like.

Moreover, thickness of film composing polyamide based film roll is alsonot particularly limited, for example, as a polyamide based film forpackaging, 8-50 μm is preferable, 10-30 μm is further preferable.

In addition, production method for obtaining a polyamide based resinfilm roll of the present invention can contain various kinds ofadditives, within the range that the characteristics are not damaged,such as lubricant, anti-blocking agent, thermal stabilizer, antioxidant,antistatic agent, light resistant agent and impact modifier. Inparticular, it is preferable to contain various kinds of inorganicparticles so as to improve lubrication of biaxially stretched film. Inaddition, as an inorganic particle, one with an average diameter ofparticle (i.e., average particle diameter) of 0.5-5.0 μm is preferable,and silica particle is particularly preferable. When the averageparticle diameter is below 0.5 μm, no good lubrication can be obtained,whereas when the average particle diameter is above 5 μm, it is notpreferable because transparency become poor and so called strike throughon printing occurs. Additionally, the average particle diameter can bemeasured by employing a method in which a weight-average diameter can becalculated from a particle distribution obtained by a coalter counter,it can be determined from the measurement of particles before additionto polyamide resin, and also can be determined from the measurement ofparticle separated by dissolving polyamide based resin film in acid.Also, an organic lubricant such as ethylene-bis-stearic acid exhibitingthe effect of lowering surface energy is preferably added becauselubrication of film composing a film roll becomes excellent.

Further, polyamide based resin film composing a film roll of the presentinvention can be subjected to thermal treatment or humidity adjustingtreatment to improve the dimensional stability according to theapplications. In addition, it can be provided with corona treatment,coating treatment or flame treatment to give better adhesion of filmsurface, and also processed by printing, deposition or the like.

Additionally, any particular one of the above-described measures (1) to(6) alone does not contribute to the reduction of variation in thephysical properties of film roll, and we are considering that, by usinga combination of measures (1) to (6), the variation in the physicalproperties of film roll can be very efficiently reduced. Then, bybringing the melted resin sheet into strongly electrostatical contactwith the cooling roll by the use of steamer corona discharge asdescribed above when unstretched sheet is formed, it is possible toreduce physical variations of the film roll even when the film is formedat a high speed.

In addition, the polyamide based resin film roll to be produced by theproducing process of the present invention provides highly uniformcharacteristics in the wind-up direction. That is, the polyamide basedresin film roll obtained by the production process of the presentinvention has an average boiling water shrinkage percentage which is theaverage of the maximum boiling water shrinkage percentages adjusted tobe 3% or more and 6% or less in the case of cutting out a sample in amethod described later, when a maximum boiling water shrinkagepercentage which is the maximum value of boiling water shrinkagepercentages in all directions for all samples is measured.

Also, in the case of cutting out a sample in a method described later,when a directional difference of boiling water shrinkage percentage of apolyamide based resin film roll to be produced by the producing processof the present invention (a polyamide based film roll of the presentinvention) is measured, the directional difference of boiling watershrinkage percentage being the difference between a boiling watershrinkage percentage in the direction of +45° to the longitudinaldirection and a boiling water shrinkage percentage in the direction of−45′ to the longitudinal direction for all samples in an absolute value,an average directional difference of boiling water shrinkage percentagewhich is the average of the directional differences of boiling watershrinkage percentage is adjusted to be 1.5% or less.

The cutout of sample in the present invention is first set up to be afirst sample cutout portion within 2 m from the winding end of film anda final cutout portion within 2 m from the winding start of film, and asample cutout portion is to be set up in approximately every 100 m fromthe first sample cutout portion. Additionally, “approximately every 100m” means that a sample may be cut out in about 100 m±1 m.

The above-mentioned cutout of sample will be more specifically describedas follows; for example, when a roll of polyamide based film is wound ina length of 498 m, a first sample (1) is cut out within 2 m from thewinding end of film. Additionally, the cutout of sample is forconvenience cut into a rectangle having a side along the longitudinaldirection and a side perpendicular to the longitudinal direction (not tobe cut out on a slant). Subsequently, a second sample (2) is cut out ina part 100 m apart toward the winding start side from the part cut out.Similarly a third sample (3) in a part 200 m apart toward the windingstart side, a fourth sample (4) in a part 300 m apart toward the windingstart side, and a fifth sample (5) in a part 400 m apart toward thewinding start side are cut out. When samples are cut out in this way,the rest becomes shorter than 100 m, thus a sixth (final) sample (6) iscut out in any part within 2 m from winding start of film. Then thefollowing values of each sample cut out are measured in the followingmethods. They are, boiling water shrinkage percentage (hereinaftercalled BS), maximum boiling water shrinkage percentage (hereinaftercalled BSx), average boiling water shrinkage percentage (hereinaftercalled BSax), directional difference of boiling water shrinkagepercentage (hereinafter called BSd) and average directional differenceof boiling water shrinkage percentage (hereinafter called BSad).

[Measuring methods of boiling water shrinkage percentage (BS), maximumboiling water shrinkage percentage (BSx), average boiling watershrinkage percentage (BSax), directional difference of boiling watershrinkage percentage (BSd) and average directional difference of boilingwater shrinkage percentage (BSad)]

A biaxially oriented polyamide based resin film cut out from each ofcutout portions of polyamide based resin film roll is cut out into asquare, allowed to stand in an atmosphere of 23° C. and 65% RH for 2hours and more. A circle centered on this sample (about 20 cm indiameter) is drawn, a longitudinal direction (direction of film drawnout) is set to be 0°, liner lines passing to the center of circle areclockwise drawn at intervals of 15° in the direction of 0 to 165°,diameter in each direction is measured as the length before treatment.Then, after the sample cut out is thermally treated in boiling water for30 minutes, it is brought back and water attached on its surface iswiped out, dried in air, allowed to stand in an atmosphere of 23° C. and65% RH for 2 hours or more, the length of linear line drawn to eachdiametrical direction is measured as the length after treatment asdescribed above. Then, according to the following formulas 1 to 5, thefollowing values are measured, which are, a BS (boiling water shrinkagepercentage), BSx (maximum boiling water shrinkage percentage), BSax(average boiling water shrinkage percentage), BSd (directionaldifference of boiling water shrinkage percentage) and BSad (averagedirectional difference of boiling water shrinkage percentage).

BS=[(length before treatment−length after treatment)/length beforetreatment]×100(%)  1

BSx=maximum shrinkage percentage (%) of values measured in 0 to 165°directions at intervals of 15°  2

BSax=summation of BSx's of all samples/number of samples  3

BSd=|(BS in 45° direction)−(BS in 135° direction)|  4

BSad=summation of BSd's of all samples/number of samples  5

Additionally, BSx value of polyamide film composing a polyamide basedfilm roll is important from the points for enhancing toughness andpinhole resistance of film itself as well as for maintaining thermalresistance in hot-water treatment for biaxially oriented polyamide basedresin film being formed in a bag-shape (it is called laminate strengthor heat-resistant laminate strength). When BSx value is less than 3%,toughness and pinhole resistance become insufficient, whereas when morethan 6%, lamination becomes poor, heat-resistant laminate strength inhot-water treatment becomes insufficient, which is not preferable.Preferable range of BSx is 3.5-5.0% for enhancing toughness, pinholeresistance, lamination property and heat-resistant laminate strength.

Also, BSd value of polyamide film composing a polyamide based film rollgreatly affects a curl phenomenon occurring in boiling water treatment.That is, the larger the BSd, the more easily a bag is warped into anotable curl. However, when BSd is suppressed to 1.5% or less,preferably 1.2% or less, warpage of bag in boiling water treatment canbe remarkably suppressed, which can prevent the occurrence of S-shapedcurl phenomenon.

Also, for a polyamide based resin film roll to be produced by theproducing process of the present invention, it is necessary that adegree of variability in the maximum boiling water shrinkage percentage(BSx) of all samples cut out is adjusted within ±2% to ±10% (2% or moreand ±10% or less) relative to the average boiling water shrinkagepercentage (BSa). Here, a degree of variability in the maximum boilingwater shrinkage percentages (BSx) of all samples means, when the maximumand the minimum in the maximum boiling water shrinkage percentages (BSx)of all samples are obtained, from which a larger value of the differencebetween either the maximum or the minimum and the average boiling watershrinkage is obtained, a ratio of which relative to the average boilingwater shrinkage percentage.

Namely, in a polyamide based resin film roll to be produced by theproducing process of the present invention, when boiling water shrinkagepercentage of samples (1) through (6) is denoted as Xn (n=1 to 6), boththe difference between Xmax, the maximum value of Xn and average boilingwater shrinkage percentage (BSax) and the difference between Xmin, theminimum value and average boiling water shrinkage percentage (BSax) arerequired to be within ±10%. In other words, |BSax-Xn| (additionally ∥indicates absolute value) are all required to be 10% or less.

Additionally, in a polyamide based resin film roll to be produced by theproducing process of the present invention, a degree of variability inthe maximum boiling water shrinkage percentages (BSx) of all samples cutout is preferably within ±9% relative to the average boiling watershrinkage percentage (BSa), more preferably within ±8%, and furtherpreferably within ±7%.

In addition, in a polyamide based resin film roll to be produced by theproducing process of the present invention, a lower degree ofvariability in the maximum boiling water shrinkage percentages (BSx) ofall samples cut out is preferable, but we are considering that the lowerlimit of the degree of variability is limited to about 2% from theconsideration of precision in the measurement.

Also, for a polyamide based resin film roll obtained by the productionprocess of the present invention, a degree of variability in thedirectional differences of boiling water shrinkage percentages (BSd) ofall samples cut out is required to be adjusted within ±2% to ±10% (2% ormore and ±10% or less) relative to the average directional difference ofboiling water shrinkage percentage (BSad) Here, a degree of variabilityin the directional differences of boiling water shrinkage percentages(BSd) of all samples means, when the maximum and the minimum in thedirectional differences of boiling water shrinkage percentages (BSd) ofall samples are obtained, from which a larger value of the differencebetween either the maximum or the minimum and the average directionaldifference of boiling water shrinkage is obtained, a ratio of which tothe average boiling water shrinkage percentage.

Namely, in a polyamide based resin film roll obtained by the productionprocess of the present invention, when directional difference of boilingwater shrinkage percentage of samples (1) through (6) is denoted as Yn(n=1 to 6), both the difference between Ymax, the maximum value of Ynand average directional difference of boiling water shrinkage percentage(BSad) and the difference between Ymin, the minimum value and averagedirectional difference of boiling water shrinkage percentage (BSad) arerequired to be within ±10%, in other words, |BSad−Yn| (additionally ∥indicates absolute value) are all required to be 10% or less.

Additionally, in a polyamide based resin film roll obtained by theproduction process of the present invention, a degree of variability inthe directional differences of boiling water shrinkage percentage (BSd)of all samples cut out is preferably within ±9% relative to the averagedirectional difference of boiling water shrinkage percentage (BSad),more preferably within ±8%, and further preferably within ±7%.

In addition, in a polyamide based resin film roll obtained by theproduction process of the present invention, a lower degree ofvariability in the directional differences of boiling water shrinkagepercentage (BSd) of all samples cut out is preferable, but we areconsidering that the lower limit of the degree of variability is limitedto about 2% from the consideration of precision in the measurement.

Also, in a polyamide based resin film roll obtained by the productionprocess of the present invention, a degree of variability in thicknessover the entire length in the longitudinal direction is required to beadjusted within ±2% to ±10% (2% or more and ±10% or less) relative tothe average thickness. Here, a degree of variability in thickness overthe entire length in the longitudinal direction means, when the maximumand the minimum in the thickness over the entire length in thelongitudinal direction of all samples are obtained, from which a largervalue of the difference between either the maximum or the minimum andthe average thickness is obtained, a ratio of which to the averagethickness.

Namely, in a polyamide based resin film roll obtained by the productionprocess of the present invention, both the difference between Tmax, themaximum value in thickness over the entire length in the longitudinaldirection and the average thickness (Ta, average thickness over theentire length in the longitudinal direction) and the difference betweenTmin, the minimum value and the average thickness (Ta) are required tobe within ±10%.

Additionally, in a polyamide based resin film roll obtained by theproduction process of the present invention, a degree of variability inthickness over the entire length in the longitudinal direction ispreferably within ±8% relative to the average thickness (Ta), morepreferably within ±6%.

In addition, in a polyamide based resin film roll obtained by theproduction process of the present invention, a lower degree ofvariability in thickness over the entire length in the longitudinaldirection is preferable, but we are considering that the lower limit ofthe degree of variability is limited to about 2% from the performance offilm forming apparatus.

In addition, in a polyamide based resin film roll obtained by theproduction process of the present invention, in the case where a sampleis cut out in the foregoing method, when refraction index (Nz) in thethickness direction of all samples are determined, an average refractionindex (Nza) which is the average of the refractive indexes is preferablyadjusted to be 1.500 or more, 1.520 or less. Additionally, the averagerefraction index is calculated by the following formula 6.

Nza=summation of Nz's of all samples/number of samples  6

Additionally, Nz value of polyamide film composing polyamide based filmroll greatly affects film grade such as laminate strength and thicknessirregularity. Thus, the requirement of average refraction index of 1.500or more and 1.520 or less is an essential requirement in use ofbiaxially oriented polyamide based resin film laminated with apolyolefin based resin film. When Nz is less than 1.500, laminatestrength with apolyolefin based resin film etc. becomes insufficient,which tends to cause peeling between the film and laminated substrate inboiling water treatment after bag forming. Moreover, the Nz is loweredsequentially in a process of biaxial stretching of unstreched polyamidebased resin film. In other words, Nz is thought to be an index ofstretching, larger Nz indicates insufficient stretching, thus a filmwith Nz of more than 1.520 remarkably displays thickness irregularitydue to insufficient stretching, giving an unsatisfactory film grade.Particularly preferable range of Nz is in a range of 1.507 to 1.516 fromthe considerations of both laminate strength and film grade.

Also, in a polyamide based resin film roll obtained by the productionprocess of the present invention, a degree of variability in therefraction index (Nz) of all samples cut out is preferably adjustedwithin ±2% relative to the average of refraction indexes (hereinaftercalled an average refraction index). Here, a degree of variability inthe refraction index (Nz) of all samples means, when the maximum and theminimum in the refraction index (Nz) of all samples are obtained, fromwhich a larger value of the difference between either the maximum or theminimum and the average refraction index is obtained, a ratio of whichto the average refraction.

Namely, in a polyamide based resin film roll obtained by the productionprocess of the present invention, when refraction index of samples (1)through (6) is denoted as Nz1 to Nz6, both the difference between Nzmax,the maximum value of Nz1 to Nz6 and the average refraction index, andthe difference between Nzmin, the minimum value of Nz1 to Nz6 and theaverage refraction index are preferably within ±2%, in other words, allof |average refraction index −Nz1| to |average refraction index −Nz6|are preferably 2% or less. Also, in a polyamide based film roll of thepresent invention, a degree of variability in the refraction index (Nz)of all samples cut out is more preferably within ±1% relative to theaverage refraction index.

In addition, in a polyamide based resin film roll obtained by theproduction process of the present invention, a lower degree ofvariability in the refraction index (Nz) of all samples cut out ispreferable, but we are considering that the lower limit of the degree ofvariability is limited to about 0.1% from the considerations ofprecision in the measurement and precision of machine.

As described above, by adjusting the maximum boiling water shrinkagepercentage and directional difference of boiling water shrinkagepercentage within given range values, and also by lowering the degree ofvariability in the maximum boiling water shrinkage percentage anddirectional difference of boiling water shrinkage percentage in onepolyamide based film roll, it becomes possible to prevent appearancedeterioration in bag forming processing and lamination processing, toconduct smooth processing with good yield ratio.

The present invention will be described in detail with reference toExamples below, the present invention is not limited to the aspects ofExamples, can be suitably modified to the extent not departing from thespirit of the present invention. Tables 1 through 3 show properties offeedstock chips A to E used in Examples, Comparative examples, ReferenceExamples and Reference Comparative examples; compositions of feedstockchips used in Examples, Comparative examples, Reference Examples andReference Comparative examples; and film forming conditions of filmrolls in Examples and Comparative examples, respectively. Additionally,chips A, C and D consist of 97.00% by weight of nylon 6 (relativeviscosity=2.8, Tg=41° C.) and 3.00% by weight of silica particle; andchips B and E consist of 96.45% by weight of nylon 6 (relativeviscosity=2.8, Tg=41° C.), 3.00% by weight of polymethaxyleneadipamide(relative viscosity=2.1), 0.15% by weight of ethylene-bis-stearamide and0.40% by weight of silica particle. In addition, silica particle addedto chips A and C has an average particle diameter of about 3.0 μm,silica particle added to chip B has an average particle diameter ofabout 1.8 μm, silica particle added to chips D and E has an averageparticle diameter of about 2.0 μm. Also, the shape of chips A to E areall elliptic cylinder, chip A and chip D, chip B and chip E have eachthe same length in major axis of cross section, minor axis of crosssection and chip length.

TABLE 1 Composition of resin etc. Lubricant Shape (average: mm)Polymethaxylene- Ethylene-bis- Particle Major axis Minor axis Nylon 6adipamide stearamide diameter Amount added of cross of cross Chip (% byweight) (% by weight) (% by weight) (μm) (% by weight) section sectionlength Chip A 97.00 — — 3.0 3.00 2.4 2.2 2.1 Chip B 96.65 3.00 0.15 1.80.40 2.5 2.2 2.2 Chip C 97.00 — — 3.0 3.00 4.5 2.2 4.8 Chip D 97.00 — —2.0 3.00 2.4 2.2 2.1 Chip E 96.45 3.00 0.15 2.0 0.40 2.5 2.2 2.2

TABLE 2 Melted sheet cooling conditions Take-up Atmosphere of speed ofElectrostatic close contact method discharge area melted sheet VoltageCurrent Temperature Humidity (m/min) Electrode Discharge (kv) (mA) (°C.) (% RH) Example 1 66 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Example 2 75 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Example 3 66 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Example 4 66 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Example 5 66 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Example 6 66 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Example 7 66 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Example 8 66 0.5 mmφ multineedle Streamer corona 11.0 ± 1.1100 45 75 Comparative 66 0.5 mmφ needle-form wire Glow 11.0 ± 1.1 100 —— example 1

TABLE 3 Film forming conditions Wind velocity of Temperature Mixingsuction of First ration of Angle of Water in chip fed longitudinalfeedstock slope of content vacuum to stretching chips (% by hopper ofchip box hopper Temperature weight) (degree) (ppm) (m/min.) (° C.) (°C.) Ratio Example 1 A/B = 5/95 70 800 5.0 ± 0.5 91 85 2.1 Example 2 A/B= 5/95 70 800 5.0 ± 0.5 91 85 2.1 Example 3 A/B = 5/95 70 800 5.0 ± 0.591 90 2.1 Example 4 A/B = 5/95 70 800 5.0 ± 0.5 91 85 2.1 Example 5 A/B= 15/85 70 800 5.0 ± 0.5 91 85 2.1 Example 6 D/E = 5/95 70 800 5.0 ± 0.591 85 2.1 Example 7 A/B = 5/95 65 800 5.0 ± 0.5 91 85 2.1 Example 8 A/B= 5/95 70 800 3.0 ± 0.5 91 85 2.1 Comparative A/B = 5/95 70 800 5.0 ±0.5 91 — — example 1 Film forming conditions Second longitudinalTransverse stretching stretching Thermal Relaxation TemperatureTemperature fixation treatment Film (° C.) Ratio (° C.) Ratio (° C.) (%)formability Example 1 70 1.6 130 4.0 213 5.0 Good Example 2 70 1.6 1304.0 216 5.0 Good Example 3 70 1.5 130 4.0 213 5.0 Good Example 4 70 1.6130 3.6 216 3.0 Good Example 5 70 1.6 130 4.0 213 5.0 Good Example 6 701.6 130 4.0 213 5.0 Good Example 7 70 1.6 130 4.0 213 5.0 Good Example 870 1.6 130 4.0 213 5.0 Good Comparative — — — — — 5.0 No example 1 good**Film formability: no good: broken when melted sheet is being taken up.

EXAMPLE 1

The above-described chips A and B were separately pre-dried whileheating at about 120° C. for about 8.0 hours using a blender apparatusof 15 kl. Each chip was sampled from the blender by a predeterminedamount and its water content was measured to find that chips A and Bboth had 800 ppm of water content. Additionally, the water content wasmeasured under the conditions of sample weight of 1 g and sample heatingtemperature of 230° C. using a Karl Fisher moisture meter (MKC-210manufactured by KYOTO Electronics Corp.).

Then, chips in each blender were separately supplied to a hopper justabove an extruder continuously by a quantitative screw feeder.Additionally, the amount supplied of chip A was 5.0% by weight and theamount supplied of chip B was 95.0% by weight. The hopper had a capacityto accommodate feedstock chip of 150 kg, the discharge rate of extruderwas 450 kg/hour. Also, the angle of slope of hopper was adjusted to 70°.Additionally, in Example 1, the polyamide based resin chip (chip A)other than the polyamide based resin chip with the largest amount usedcomprises each its average major axis, average minor axis and averagechip length within a range of ±20% relative to the average major axis,average minor axis and average chip length of the polyamide based resinchip with the largest amount used (chip B).

Also, on feeding chips A and B into a hopper, the chips were fed in ashort period of time from drying to the hopper so that the temperatureof chip in each blender did not become too low. The temperature of bothchips A and B just before being fed into the hopper was about 91° C.Then, the chips A and B fed were blended in the hopper, melt-extrudedthrough a T-die at 270° C. from a single screw type extruder, wound on arotating metal roll chilled at 17° C. for quenching to give anunstretched film having a thickness of 257 μm. Additionally, take-upspeed of unstretched film (rotational speed of metal roll) was about 60m/min.

Also, air gap in winding melted resin on a metal roll was adjusted to 40mm, and by applying a 100-mA direct current negative charge to themelted resin (sheet-form material) at 11±1.1 kv with a multineedleelectrode with 1.5 mmφ needle-form materials placed side by side toyield streamer corona discharge, melted resin was electrostaticallyattached closely on the metal roll. In addition, in the streamer coronadischarge described above, the periphery of the electrode and metal rollwere surrounded with the wall members to block off from the outside, thehumidity around the multineedle-shape electrode was kept to about 75%RH, and the temperature around the multineedle-shape electrode was keptto about 45° C. Furthermore, in winding melted resin on a metal roll,the part contacting the melted resin with the metal roll was sucked overthe entire width of melted resin using a vacuum box in the oppositedirection to the direction of winding the resin to advance close contactof the melted resin on the metal roll. Additionally, the wind velocityof suction in the vacuum box was adjusted to be 5.0±0.5 m/sec. over theentire width of suction inlet (i.e., entire width of melted resin). Bythe way, in producing the unstretched film described above, no adhesionof oligomer to the multineedle electrode was observed and theelectrostatically close contact condition was remarkably stable.

Thereafter, the resultant unstretched film was longitudinally stretched(first longitudinal stretching) in stretching temperature of about 85°C. and about 2.1 times by a Teflon roll (registered trademark), thenlongitudinally stretched (second longitudinal stretching) in stretchingtemperature of about 70° C. and about 1.6 times by a ceramic roll.Further, the longitudinal stretched sheet was continuously led to atenter, transversely stretched at about 130° C. and 4.0 times, thermallyfixed at about 213° C., subjected to transverse relaxation treatment of5.0% and then cooled, by cutting the both edge parts to eliminate,thereby to form a biaxially stretched film of about 15 μm and 2000 m ormore continuously and produce a mill roll. Additionally, the variationwidths of film surface temperature when a film is produced continuouslyin 2000 m were within ±0.8° C. to the average temperature in thepre-heating step, ±0.6° C. to the average temperature in the stretchingstep and ±0.5° C. to the average temperature in the thermal treatmentstep. Further, the resultant mill roll was slit into 400 mm in width and2000 m in length, and wound up on 3 inch paper tube to give twopolyamide based resin film rolls (slit rolls). Then, using the two slitrolls thus obtained (namely, obtained from the same mill roll), thecharacteristics were evaluated in the following methods. Additionally,for the following measurements of BS (boiling water shrinkagepercentage), BSx (maximum boiling water shrinkage percentage), BSd(directional difference of boiling water shrinkage percentage) andrefraction index, sample films were prepared as follows: a first samplecutout portion was set up within 2 m from the winding end of film,sample cutout portions from a second to 20th were set up inapproximately every 100 m from the first sample cutout portion, a 21stcutout portion was set up within 2 m from the winding start of film, andsample films were cut out from each of cutout portions from the first tothe 21st. The evaluation results are shown in Tables 4 to 8. In showingthe evaluation results, an average of values of each sample measured andvariation range of values of each sample are shown for impact strengthand laminate strength. Also, regarding the S-shaped curl, the numbers ofsamples determined in each evaluation level and the total evaluationlevel of all samples are shown.

[Boiling Water Shrinkage Percentage]

A biaxially oriented polyamide based resin film (sample film) cut outfrom each of cutout portions of one slit roll was cut out in a squarewith a side of 21 cm, allowed to stand in an atmosphere of 23° C. and65RH % for two hours or more. A circle of about 20 cm in diametercentered on this sample was drawn, a longitudinal direction (directionof film drawn out) was set to be 0°, liner lines passing to the centerof circle were clockwise drawn at intervals of 15° in the direction of 0to 165°, and diameter in each direction was measured as the lengthbefore treatment. Then, after the sample cut out was thermally treatedin boiling water for 30 minutes, it was brought back and water attachedon the surface was wiped out, dried in air, allowed to stand in anatmosphere of 23° C. and 65% RH for 2 hours or more, as described above,and the length of linear line drawn to each diametrical direction wasmeasured as the length after treatment. Then, according to the foregoingformulas 1 to 5, the following values were measured, which were, the BS(boiling water shrinkage percentage), BSx (maximum boiling watershrinkage percentage), BSax (average boiling water shrinkagepercentage), BSd (directional difference of boiling water shrinkagepercentage) and BSad (average directional difference of boiling watershrinkage percentage).

Thereafter, the maximum and the minimum of the maximum boiling watershrinkage percentage (BSx) of all samples were obtained, a largerdifference between either the maximum or the minimum and the averageboiling water shrinkage percentage (BSax) was calculated, a ratio ofwhich relative to the average boiling water shrinkage percentage (BSax)was calculated, and thereby a degree of variability in the maximumboiling water shrinkage percentage (BSx) relative to the average boilingwater shrinkage percentage (BSax) was obtained. Also, the maximum andthe minimum of the directional difference of boiling water shrinkagepercentage (BSd) of all samples were obtained, a larger differencebetween either the maximum or the minimum and the average directionaldifference of boiling water shrinkage percentage (BSad) was calculated,a ratio of which relative to the average directional difference ofboiling water shrinkage percentage (BSad) was calculated, and thereby adegree of variability in the directional difference of boiling watershrinkage percentage (BSd) relative to the average directionaldifference of boiling water shrinkage percentage (BSad) was obtained.

[Thickness Irregularity in the Longitudinal Direction]

A slit roll for measurement of thickness irregularity was prepared byslitting a slit roll in about 3 cm width over the entire length in thelongitudinal direction. Then, the average thickness, the maximumthickness and the minimum thickness were obtained over the entire lengthin the longitudinal direction using a thickness irregularity measuringapparatus (wide range high sensitive electronic micrometer K-313A)manufactured by Anritsu Corp. Thereafter, from the following formula 7,a degree of variability in thickness over the entire length in thelongitudinal direction was calculated as follows: a larger differencebetween either the maximum thickness or the minimum thickness and theaverage thickness was calculated, a ratio of which relative to theaverage thickness was calculated to give the degree of variability inthickness over the entire length in the longitudinal direction.

Degree of variability in thickness=|maximum thickness or minimumthickness−average thickness|/average thickness  7

[Lamination Processability]

Using another slit roll (obtained from the same mill roll) differentfrom a slit roll by which the above-described boiling water shrinkagepercentage, thickness irregularity in the longitudinal direction,refraction index and impact strength were measured, a laminated filmroll with a three layer laminated structure consisting of polyamidebased resin/LDPE/LLDPE was obtained as follows: to a biaxially orientedpolyamide resin film composing the slit roll, urethane based AC agent(“EL443” manufactured by Toyo-Morton, Ltd.) was coated, and then, onwhich LDPE (low density polyethylene) film of 15 μm in thickness wascontinuously extruded at 315° C. using a single test laminator apparatusmanufactured by Modern Machinery Ltd., and further LLDPE (linear lowdensity polyethylene) film of 40 μm in thickness was continuouslylaminated thereon. Also, processability in producing a laminated filmroll was evaluated as the following three levels.

O: no wrinkle of roll occurs, so no need in adjustment of conditionΔ: wrinkle of roll eliminated by adjustment of conditionX: wrinkle of roll still occurs in spite of any adjustment of condition

[Refraction Index]

Using an “Abbe refractometer 4T type” manufactured by Atago Co., Ltd,each sample film cut out from each of cutout portions was allowed tostand in an atmosphere of 23° C. and 65RH % for 2 hours or more, thenrefraction index in the thickness direction (Nz) was measured. Also, theaverage refraction index of all samples was calculated, as shown inTable 6, the difference between either the maximum or the minimum of Nzin all samples and the average refraction index was calculated and aratio of which relative to the average refraction index was calculatedas a degree of variability.

[S-Shaped Curl Phenomenon]

As described above, the laminate film wound out as a laminate film rollwas two folded parallel to the winding length direction whilecontinuously conducting heat-sealing on each of both edges in 20 mm at150° C. in the longitudinal direction using a test sealer manufacturedby Nishibe Kikai Co. Ltd. Then, the film was intermittently heat-sealedat intervals of 150 mm in 10 mm in the perpendicular direction theretoto obtain a half-finished product with width of 200 mm. This product wascut in the winding length direction so that both edges have a sealedpart of 10 mm, then cut at the boundary of the sealed part in theperpendicular direction thereto, and thereby to prepare a three-edgesealed bag (seal width: 10 mm). Of the three-edge sealed bags, thethree-edge sealed bag prepared from the portion within 2 m from windingend of laminate film roll was selected as a first sample, and thethree-edge sealed bags prepared from the portions being about 100, 200,. . . 1900 m apart from the prepared portion of the first sample wereselected as a second to 20th sample, respectively, and the three-edgesealed bag prepared from the portion within 2 m from winding start oflaminate film roll was selected as a 21st sample. Thereafter, thesetwenty-one three-edge sealed bags were thermally treated in boilingwater for 30 minutes, then allowed to stand in an atmosphere of 23° C.and 65RH % overnight, and further, the twenty-one three-edge sealed bagswere overlapped, and 1 kg load was applied on the entire surface of bagfrom above, being kept overnight, and followed by removing the load. Thedegree of warpage of bag (S-shaped curl) was evaluated as follows.

⊚: no warpage at allO: warpage is slightly observedX: warpage is apparently observedXX: remarkable warpage

[Impact Strength]

Each sample film cut out from each of cutout portions was allowed tostand in an atmosphere of 23° C. and 65RH % for 2 hours or more, thenbreaking strength was measured using a “Film impact tester TSS type”manufactured by Toyo Seiki Seisaku-Sho, Ltd. with hemispheric collisionball of 12.7 mm in diameter, and the strength was defined as impactstrength. The average impact strength of all sample films was alsocalculated.

[Laminate Strength]

Also, a laminate film cut out from the laminate film roll was cut out in15 mm wide and 200 mm long as a sample piece, and peel strength betweenpolyamide based resin film layer and LDPE layer was measured under theconditions of temperature of 23° C. and relative humidity of 65% using“Tensiron UMT-II-500 type” manufactured by Toyo Boldwin Co. Ltd.Additionally, pulling rate was 10 cm/min., peeling angle was 180 degree,and the measurement was carried out with a peeling part immersed inwater. Also, in the measurement of laminate strength, a first samplepiece was cut out within 2 m from the winding end of laminate film roll,sample pieces of a second to 20th were cut out in approximately every100 m from the first sample cutout portion, a 21st sample piece was cutout within 2 m from the winding start of film, and each sample piecefrom the first to the 21st was measured. The average of the measurementswas also calculated.

EXAMPLE 2

A polyamide based resin film roll of Example 2 was obtained in the samemanner as in the case of Example 1, except for changing the take-upspeed of the sheet in a melted state to 75 m/min and the thermalfixation temperature after biaxial extension to about 216° C. Then, thecharacteristics of the obtained film roll was evaluated in the methodsame as that of Example 1. Table 4 through 8 show the evaluationresults.

EXAMPLE 3

An unstretched film obtained in the same manner as in Example 1 waslongitudinally stretched (first longitudinal stretching) at stretchingtemperature of about 90° C. and about 2.2 times by a Teflon (registeredtrademark) roll, and then longitudinally stretched (second longitudinalstretching) at stretching temperature of about 70° C. and about 1.5times by a ceramic roll. Further, in the same manner as in Example 1,the longitudinally stretched sheet was continuously led to a stenter,and transversely stretched at about 130° C. and 4.0 times. Then, it wasthermally fixed at about 213° C., subjected to transverse relaxationtreatment of 5.0% and cooled. Then, by cutting the both edge parts toeliminate, a biaxially stretched film of about 15 μm and 2000 m or morecontinuously was formed. Additionally, the variation width of filmsurface temperature when the film was continuously produced was the sameas in Example 1. The obtained film was slit and wound up in the samemanner as in Example 1, to give polyamide based resin film rolls inExample 3. Then, the characteristics of the obtained film rolls wereevaluated in the same methods as in Example 1. The evaluation resultsare shown in Tables 4 to 8.

EXAMPLE 4

An unstretched film obtained in the same manner as in Example 1 waslongitudinally stretched in two stages in the same manner as inExample 1. Thereafter, the longitudinally stretched sheet continuouslyled to a stenter, transversely stretched at about 130° C. and 3.6 times.Then, it was thermally fixed at about 216° C., subjected to transverserelaxation treatment of 3.0% and cooled. Then, by cutting the both edgeparts to eliminate, a biaxially stretched film of about 15 μm and 2000 mor more continuously was formed. Additionally, the variation width offilm surface temperature when the film was continuously produced was thesame as in Example 1. The obtained film was slit and wound up in thesame manner as in Example 1, to give polyamide based resin film rolls inExample 4. Then, the characteristics of the obtained film roll wereevaluated in the same methods as in Example 1. The evaluation resultsare shown in Tables 4 to 8.

EXAMPLE 5

A polyamide based resin film roll in Example 5 was obtained in the samemanner as in Example 1 except that the mixing ratio of feedstock chip Aand feedstock chip B was set chip A to 15.0% by weight and chip B to85.0% by weight. Additionally, also in Example 5, the polyamide basedresin chip (chip A) other than the polyamide based resin chip with thelargest amount used comprises each its average major axis, average minoraxis and average chip length within a range of ±20%, respectively,relative to the average major axis, average minor axis and average chiplength of the polyamide based resin chip with the largest amount used(chip B). Then, the characteristics of the obtained film roll wereevaluated in the same methods as in Example 1. The evaluation resultsare shown in Tables 4 to 8.

EXAMPLE 6

A polyamide based resin film roll in Example 6 was obtained in the samemanner as in Example 1 except that feedstock chips D and E were usedinstead of feedstock chips A and B, respectively (namely in Example 6, apolyamide based resin film roll was produced using chip D of 5.0% byweight and chip E of 95.0% by weight). Additionally, also in Example 6,the polyamide based resin chip (chip b) other than the polyamide basedresin chip with the largest amount used comprises each its average majoraxis, average minor axis and average chip length within a range of ±20%relative to the average major axis, average minor axis and average chiplength of the polyamide based resin chip with the largest amount used(chip E). Then, the characteristics of the obtained film roll wereevaluated in the same methods as in Example 1. The evaluation resultsare shown in Tables 4 to 8.

EXAMPLE 7

A polyamide based resin film roll in Example 7 was obtained in the samemanner as in Example 1 except that an angle of slope of hopper waschanged to 65° on supplying feedstock chip in a blender into a hopperjust above an extruder. Then, the characteristics of the obtained filmroll were evaluated in the same methods as in Example 1. The evaluationresults are shown in Tables 4 to 8.

EXAMPLE 8

A polyamide based resin film roll in Example 8 was obtained in the samemanner as in Example 1 except that wind velocity of suction in a vacuumbox was adjusted to 3.0±0.5 m/sec. over the entire width of suctioninlet in winding melted resin on a metal roll. Then, the characteristicsof the obtained film roll were evaluated in the same methods as inExample 1. The evaluation results are shown in Tables 4 to 8.

COMPARATIVE EXAMPLE 1

When a melted resin was brought into electrostatically close contactwith a metal roll, the electrode was changed to 0.5 mm+wire with therotation speed of the metal roll kept to about 66 m/min and 100 mA dcnegative charge was applied to the melted resin at 11±1.1 kv to carryout glow discharge; the melted resin winding on the wire and was unableto be brought in electrostatically close contact with the metal roll,and unstretched film that could be stretched was unable to be obtained.

TABLE 4 Characteristics of polyamide based resin film roll Degree ofvariability in Maximum or maximum boiling minimum of water shrinkageAverage boiling maximum boiling percentage to water shrinkage watershrinkage average boiling percentage percentage of all water percentage*(BSax: %) samples (%) (%) Example 1 4.3 4.6 7.0 Example 2 4.5 4.7 4.4Example 3 3.9 3.6 7.7 Example 4 3.5 3.8 8.6 Example 5 3.7 4.0 8.1Example 6 4.0 4.2 5.0 Example 7 4.2 4.5 7.1 Example 8 4.8 4.5 6.3Comparative — — — example 1 *Degree of variability in maximum boilingwater shrinkage percentage to average boiling water shrinkagepercentage:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum of maximum boiling water shrinkagepercentage of all samples and the average boiling water shrinkagepercentage.

TABLE 5 Characteristics of polyamide based resin film roll Degree ofvariability in directional difference of boiling water Maximum orshrinkage Average minimum of percentage to directional directionalaverage difference of difference of directional boiling water boilingwater difference of shrinkage shrinkage boiling water percentagepercentage of all shrinkage (BSad: %) samples (%) percentage* (%)Example 1 1.3 1.2 7.7 Example 2 1.2 1.3 8.3 Example 3 1.2 1.3 8.3Example 4 1.3 1.2 7.7 Example 5 1.0 1.1 10.0  Example 6 1.1 1.1 0.0Example 7 1.4 1.5 7.1 Example 8 1.4 1.3 7.1 Comparative — — — example 1*Degree of variability in directional difference of boiling watershrinkage percentage to average directional difference of boiling watershrinkage percentage:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum of directional difference of boilingwater shrinkage percentage of all samples and the average directionaldifference of boiling water shrinkage percentage.

TABLE 6 Characteristics of polyamide based resin film roll Degree ofMaximum or variability in minimum of thickness to Average thicknessthickness throughout average (μm) full length (μm) thickness* (%)Example 1 15.01 14.45 3.7 Example 2 14.98 15.88 6.0 Example 3 15.0514.31 4.9 Example 4 15.05 14.25 5.3 Example 5 14.95 15.98 6.9 Example 614.98 15.70 4.8 Example 7 15.02 16.15 7.5 Example 8 15.03 16.25 8.1Comparative — — — example 1 *Degree of variability in thickness toaverage thickness:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum of thickness throughout the fulllength and the average length.

TABLE 7 Characteristics of polyamide based resin film roll Degree ofvariability in Maximum or refraction index minimum of to average Averagerefraction refraction indexes of refraction index (Nz) all samplesindex* (%) Example 1 1.511 1.518 0.5 Example 2 1.510 1.505 0.3 Example 31.512 1.505 0.5 Example 4 1.512 1.508 0.3 Example 5 1.510 1.515 0.3Example 6 1.512 1.518 0.4 Example 7 1.512 1.507 0.3 Example 8 1.5111.519 0.5 Comparative — — — example 1 *Degree of variability inrefraction index to average refraction index:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum of refraction indexes of all samplesand the average refraction index.

TABLE 8 Evaluation result Impact Laminate S-shaped curl strength (kg/cm)strength (g/15 mm) Sample numbers each of Variation Variation LaminationTotal ⊚, ◯, X Average range Average range processability Example 1 ⊚ ⊚ .. . 20, ◯ . . . 1 11.6 10.8-12.2 210 200-220 ◯ Example 2 ⊚ ⊚ . . . 18, ◯. . . 3 11.4 10.6-12.0 210 200-220 ◯ Example 3 ◯ ⊚ . . . 6, ◯ . . . 1510.7 10.1-11.3 210 200-220 ◯ Example 4 ⊚ ⊚ . . . 20, ◯ . . . 1 13.212.5-13.7 300 280-320 ◯ Example 5 ⊚ ⊚ . . . 16, ◯ . . . 5 10.2 9.9-10.6200 180-220 ◯ Example 6 ⊚ ⊚ . . . 19, ◯ . . . 2 11.2 10.8-11.9 230220-240 ◯ Example 7 ⊚ ⊚ . . . 18, ◯ . . . 3 11.0 10.2-11.7 230 220-240 ◯Example 8 ⊚ ⊚ . . . 16, ◯ . . . 5 11.2 10.8-11.9 200 180-220 ◯Comparative — — — — — — — example 1

REFERENCE EXAMPLE 1

A polyamide based resin film roll of reference example 1 was obtained inthe same manner as Example 1, except that the take-up speed (metal rollrotating speed) of the resin sheet when the melted resin was broughtinto electrostatically closed contact to the metal roll was changed to60 m/min and the electrostatically close contact method was changed toglow discharge (100 mA dc negative charge applied at 11±1.1 kv) by a 0.5mmφ wire electrode as well as thermal fixation temperature after biaxialstretching to about 210° C. Additionally, The variation range of thefilm surface temperature when the film was continuously produced waswithin the range of average temperature ±0.8° C. in the preheatingprocess, average temperature of ±0.6° C. in the stretching process, andaverage temperature ±0.5° C. in the heat treatment process as with thesame manners as Example 1. Then, the characteristics of the obtainedfilm roll were evaluated by the method same as that of Referenceexample 1. Tables 9 and 10 show the producing conditions of the filmroll in Reference Example 1 and Tables 11 through 15 show the evaluationresults of film roll characteristics.

REFERENCE EXAMPLE 2

An unstretched film obtained in the same manner as in Reference example1 was longitudinally stretched (first longitudinal stretching) atstretching temperature of about 90° C. and about 2.2 times by a Teflon(registered trademark) roll, and then longitudinally stretched (secondlongitudinal stretching) at stretching temperature of about 70° C. andabout 1.5 times by a ceramic roll. Further, in the same manner as inReference example 1, the longitudinally stretched sheet was continuouslyled to a stenter, and transversely stretched at about 130° C. and 4.0times. Then, it was thermally fixed at about 210° C., subjected totransverse relaxation treatment of 5.0% and cooled. Then, by cutting theboth edge parts to eliminate, a biaxially stretched film of about 15 μmand 2000 m or more continuously was formed. Additionally, the variationrange of film surface temperature when the film was continuouslyproduced was the same as in Reference example 1. The obtained film wasslit and wound up in the same manner as in Reference example 1 andpolyamide based resin film rolls of Reference example 2 was obtained.Then, the characteristics of the obtained film rolls were evaluated inthe same methods as in Example 1. Tables 9 and 10 show the producingconditions of the film roll in Reference example 2 and Tables 11 through15 show the evaluation results.

REFERENCE EXAMPLE 3

An unstretched film obtained in the same manner as in Reference example1 was longitudinally stretched in two stages in the same manner as inReference example 1. Thereafter, the longitudinally stretched sheetcontinuously led to a stenter, transversely stretched at about 130° C.and 3.6 times. Then, it was thermally fixed at about 215° C., subjectedto transverse relaxation treatment of 3.0% and cooled. Then, by cuttingthe both edge parts to eliminate, a biaxially stretched film of about 15μm and 2000 m or more continuously was formed. Additionally, thevariation width of film surface temperature when the film wascontinuously produced was the same as in Reference example 1. Theobtained film was slit and wound up in the same manner as in Referenceexample 1, and polyamide based resin film rolls of Reference example 3was obtained. Then, the characteristics of the obtained film roll wereevaluated in the same methods as in Example 1. Tables 9 and 10 showproducing conditions of film roll of Reference example 3 and Tables 11through 15 show the evaluation results of film roll characteristics.

REFERENCE EXAMPLE 4

A polyamide based resin film roll in Reference example 4 was obtained inthe same manner as in Reference example 1 except that the mixing ratioof feedstock chip A and feedstock chip B was set in chip A of 15.0% byweight and chip B of 85.0% by weight. Additionally, also in Referenceexample 4, the polyamide based resin chip (chip A) other than thepolyamide based resin chip with the largest amount used includes,respectively, its average major axis, average minor axis and averagechip length within a range of ±20% relative to the average major axis,average minor axis and average chip length of the polyamide based resinchip with the largest amount used (chip B). Then, the characteristics ofthe obtained film roll were evaluated in the same methods as inExample 1. Tables 9 and 10 show the producing conditions of the filmroll in Reference example 4 and Tables 11-15 show evaluation results offilm roll characteristics.

REFERENCE EXAMPLE 5

A polyamide based resin film roll in Reference example 5 was obtained inthe same manner as in Reference example 1 except that feedstock chips Dand E were used instead of feedstock chips A and B, respectively, namelyin Reference example 5, a polyamide based resin film roll was producedusing chip D of 5.0% by weight and chip E of 95.0% by weight.Additionally, also in Reference example 5, the polyamide based resinchip (chip D) other than the polyamide based resin chip with the largestamount used comprises each its average major axis, average minor axisand average chip length within a range of ±20% relative to the averagemajor axis, average minor axis and average chip length of the polyamidebased resin chip with the largest amount used (chip E). Then, thecharacteristics of the obtained film roll were evaluated in the samemethods as in Example 1. Tables 9 and 10 show film roll manufacturingconditions in Reference example 5 and Tables 11-15 show evaluationresults of film roll characteristics.

REFERENCE EXAMPLE 6

A polyamide based resin film roll in Reference example 6 was obtained inthe same manner as in Reference example 1 except that an angle of slopeof hopper was changed to 65° on supplying feedstock chip in a blenderinto a hopper just above an extruder. Then, the characteristics of theobtained film roll were evaluated in the same methods as in Example 1.Tables 9 and 10 show film roll manufacturing conditions in Referenceexample 6 and Tables 11 to 15 show evaluation results of film rollcharacteristics.

REFERENCE EXAMPLE 7

A polyamide based resin film roll in Reference example 7 was obtained inthe same manner as in Reference example 1 except that wind velocity ofsuction in a vacuum box was adjusted to 3.0±0.5 m/sec. over the entirewidth of suction inlet in winding melted resin on a metal roll. Then,the characteristics of the obtained film roll were evaluated in the samemethods as in Example 1. Tables 9 and 10 show film roll manufacturingconditions in Reference example 7 and Tables 11 to 15 show evaluationresults of film roll characteristics.

REFERENCE COMPARATIVE EXAMPLE 1

An unstretched film obtained in the same manner as in Example 1 waslongitudinally stretched (first longitudinal stretching) at stretchingtemperature of about 90° C. and about 1.5 times by a Teflon (registeredtrademark) roll, then longitudinally stretched (second longitudinalstretching) at stretching temperature of about 70° C. and about 2.2times by a ceramic roll. Further, the longitudinally stretched sheet wascontinuously led to a stenter, in the same manner as in Referenceexample 1, transversely stretched, thermally fixed, subjected totransverse relaxation treatment and cooled. Then, by cutting the bothedge parts to eliminate, a biaxially stretched film of about 15 μm and2000 m or more continuously was formed. Additionally, the variationwidth of film surface temperature when the film was continuouslyproduced was the same as in Reference example 1. Thereafter, theobtained film was slit and wound up in the same manner as in Referenceexample 1 and polyamide based resin film rolls of Reference comparativeexample 1 was obtained. Then, the characteristics of the obtained filmroll were evaluated in the same methods as in Example 1. Tables 9 and 10show the producing conditions of the film roll in Reference comparativeexample 1 and Tables 11 to 15 show evaluation results of film rollcharacteristics.

REFERENCE COMPARATIVE EXAMPLE 2

A polyamide based resin film roll in Reference comparative example 2 wasobtained in the same manner as in Reference example 1 except thatfeedstock chip C was used instead of feedstock chip A. Additionally, inReference comparative example 2, the polyamide based resin chip (chip C)other than the polyamide based resin chip with the largest amount usedcomprises each its average major axis and average chip length outsidethe range of ±20% relative to the average major axis and average chiplength of the polyamide based resin chip with the largest amount used(chip B). Then, the characteristics of the obtained film roll wereevaluated in the same methods as in Example 1. Tables 9 and 10 show theproducing conditions of the film roll in Reference comparative example 2and Tables 11 to 15 show evaluation results of film rollcharacteristics.

REFERENCE COMPARATIVE EXAMPLE 3

A polyamide based resin film roll in Reference comparative example 3 wasobtained in the same manner as in Reference example 1 except thatpre-drying condition of feedstock chips A and B was changed to a methodof heating at about 100° C. for about 4.0 hours. Additionally, apredetermined amount of each chip was sampled from the inside of ablender after pre-drying, water content was measured, which showed thatthe water contents of chips A and B were both 1500 ppm, and thetemperatures of chips A and B just before being fed to the hopper wereboth at about 85° C. Then, the characteristics of the obtained film rollwere evaluated in the same methods as in Example 1. Tables 9 and 10 showthe producing conditions of the film roll in Reference comparativeexample 3 and Tables 11 to 15 show evaluation results of film rollcharacteristics.

REFERENCE COMPARATIVE EXAMPLE 4

A polyamide based resin film roll in Reference comparative example 4 wasobtained in the same manner as in Reference example 1 except thatfeedstock chips A and B were allowed to stand in each of blenders forabout 5 hours after pre-drying before being fed into a hopper just abovean extruder. Additionally, the water contents of chips A and B were both800 ppm just before being fed to a hopper, and the temperatures of chipsA and B just before being fed to a hopper were both about 30° C. Then,the characteristics of the obtained film roll were evaluated in the samemethods as in Example 1. Tables 9 and 10 show the producing conditionsof the film roll in Reference comparative example 4 and Tables 11 to 15show evaluation results of film roll characteristics.

REFERENCE COMPARATIVE EXAMPLE 5

A polyamide based resin film roll in Reference comparative example 5 wasobtained in the same manner as in Reference example 1 except that nosuction was conducted by a vacuum box in winding melted resin on a metalroll. Then, the characteristics of the obtained film roll were evaluatedin the same methods as in Example 1. Tables 9 and 10 show film rollmanufacturing conditions in Reference comparative example 5 and Tables11-15 show evaluation results of film roll characteristics.

TABLE 9 Cooling conditions of melted sheet Take-up speed of meltedElectrostatic close contact method sheet Voltage Current (m/min)Electrode Discharge (kv) (mA) Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100example 1 needle form wire Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100example 2 needle form wire Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100example 3 needle form wire Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100example 4 needle form wire Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100example 5 needle form wire Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100example 6 needle form wire Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100example 7 needle form wire Reference 60 0.5 mmφ Glow 11.0 ± 1.1 100Comparative needle example 1 form wire Reference 60 0.5 mmφ Glow 11.0 ±1.1 100 Comparative needle example 2 form wire Reference 60 0.5 mmφ Glow11.0 ± 1.1 100 Comparative needle example 3 form wire Reference 60 0.5mmφ Glow 11.0 ± 1.1 100 Comparative needle example 4 form wire Reference60 0.5 mmφ Glow 11.0 ± 1.1 100 Comparative form wire example 5

TABLE 10 Film forming conditions Wind velocity of Temperature Mixingsuction of First ration of Angle of Water in chip fed longitudinalfeedstock slope of content vacuum to stretching chips (% by hopper ofchip box hopper Temperature weight) (degree) (ppm) (m/min.) (° C.) (°C.) Ratio Reference A/B = 5/95 70 800 5.0 ± 0.5 91 85 2.1 example 1Reference A/B = 5/95 70 800 5.0 ± 0.5 91 90 2.2 example 2 Reference A/B= 5/95 70 800 5.0 ± 0.5 91 85 2.1 example 3 Reference A/B = 15/85 70 8005.0 ± 0.5 91 85 2.1 example 4 Reference D/E = 5/95 70 800 5.0 ± 0.5 9185 2.1 example 5 Reference A/B = 5/95 65 800 5.0 ± 0.5 91 85 2.1 example6 Reference A/B = 5/95 70 800 3.0 ± 0.5 91 85 2.1 example 7 ReferenceA/B = 5/95 70 800 5.0 ± 0.5 91 90 1.5 Comparative example 1 ReferenceC/B = 5/95 70 800 5.0 ± 0.5 91 85 2.1 Comparative example 2 ReferenceA/B = 5/95 70 1500  5.0 ± 0.5 85 85 2.1 Comparative example 3 ReferenceA/B = 5/95 70 800 5.0 ± 0.5 30 85 2.1 Comparative example 4 ReferenceA/B = 5/95 70 800 — 91 85 2.1 Comparative example 5 Film formingconditions Second longitudinal Transverse stretching stretching ThermalRelaxation Temperature Temperature fixation treatment Film (° C.) Ratio(° C.) Ratio (° C.) (%) formability Reference 70 1.6 130 4.0 210 5.0Good example 1 Reference 70 1.5 130 4.0 210 5.0 Good example 2 Reference70 1.6 130 3.6 215 3.0 Good example 3 Reference 70 1.6 130 4.0 210 5.0Good example 4 Reference 70 1.6 130 4.0 210 5.0 Good example 5 Reference70 1.6 130 4.0 210 5.0 Good example 6 Reference 70 1.6 130 4.0 210 5.0Good example 7 Reference 70 2.2 130 4.0 210 5.0 Good Comparative example1 Reference 70 1.6 130 4.0 210 5.0 Good Comparative example 2 Reference70 1.6 130 4.0 210 5.0 Good Comparative example 3 Reference 70 1.6 1304.0 210 5.0 Good Comparative example 4 Reference 70 1.6 130 4.0 210 5.0Good Comparative example 5

TABLE 11 Characteristics of polyamide based resin film roll Degree ofvariability in Average maximum boiling boiling water shrinkage waterMaximum or minimum of percentage to shrinkage maximum boiling wateraverage boiling percentage shrinkage percentage water shrinkage (BSax:%) of all samples (%) percentage* (%) Reference 4.2 4.5 7.1 example 1Reference 3.8 4.1 7.9 example 2 Reference 3.2 3.0 6.3 example 3Reference 3.5 3.7 5.7 example 4 Reference 4.0 4.3 7.5 example 5Reference 4.0 3.7 7.5 example 6 Reference 5.1 5.5 7.8 example 7Reference 5.0 4.6 8.0 Comparative example 1 Reference 5.7 5.1 10.5Comparative example 2 Reference 6.3 6.9 9.5 Comparative example 3Reference 5.5 5.0 9.1 Comparative example 4 Reference 4.2 4.7 11.9Comparative example 5 *Degree of variability in maximum boiling watershrinkage percentage to average boiling water shrinkage percentage:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum boiling water shrinkage percentage ofall samples and the average boiling water shrinkage percentage.

TABLE 12 Characteristics of polyamide based resin film roll Maximum orDegree of variability Average minimum in directional directional ofdirectional difference of boiling difference difference of watershrinkage of boiling boiling water percentage to average water shrinkagedirectional difference shrinkage percentage of boiling water percentageof all shrinkage (BSad: %) samples (%) percentage* (%) Reference example1 1.2 1.3 8.3 Reference example 2 1.4 1.5 7.1 Reference example 3 1.41.5 7.1 Reference example 4 1.1 1.0 9.1 Reference example 5 1.1 1.0 9.1Reference example 6 1.3 1.4 7.7 Reference example 7 1.4 1.3 7.1Reference 1.6 1.4 12.5 Comparative example 1 Reference 1.3 1.5 15.4Comparative example 2 Reference 1.8 1.6 11.1 Comparative example 3Reference 1.5 1.7 13.3 Comparative example 4 Reference 1.7 1.9 11.8Comparative example 5 *Degree of variability in directional differenceof boiling water shrinkage percentage to average directional differenceof boiling water shrinkage percentage:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum of directional difference of boilingwater shrinkage percentage of all samples and the average directionaldifference of boiling water shrinkage.

[Table 13]

TABLE 6 Characteristics of polyamide based resin film roll Degree ofMaximum or variability in minimum of thickness to Average thicknessthickness throughout average (μm) full length (μm) thickness* (%)Reference 15.03 15.80 5.1 example 1 Reference 15.05 15.82 5.1 example 2Reference 15.03 15.75 4.8 example 3 Reference 15.05 16.05 6.6 example 4Reference 15.05 15.64 3.9 example 5 Reference 15.04 16.18 7.6 example 6Reference 15.04 16.24 8.0 example 7 Reference 15.05 17.32 15.1Comparative example 1 Reference 15.05 15.99 6.2 Comparative example 2Reference 15.03 13.75 8.6 Comparative example 3 Reference 15.05 13.5110.2 Comparative example 4 Reference 15.05 16.92 12.4 Comparativeexample 5 *Degree of variability in thickness to average thickness:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum of thickness throughout the fulllength and the average length.

TABLE 14 Characteristics of polyamide based resin film roll Degree ofvariability in Maximum or refraction index minimum of to average Averagerefraction refraction indexes of refraction index (Nz) all samplesindex* (%) Reference 1.510 1.518 0.5 example 1 Reference 1.512 1.505 0.5example 2 Reference 1.514 1.508 0.4 example 3 Reference 1.510 1.518 0.5example 4 Reference 1.510 1.515 0.3 example 5 Reference 1.512 1.519 0.5example 6 Reference 1.510 1.519 0.6 example 7 Reference 1.511 1.494 1.1Comparative example 1 Reference 1.511 1.519 0.5 Comparative example 2Reference 1.508 1.517 0.6 Comparative example 3 Reference 1.512 1.5230.7 Comparative example 4 Reference 1.510 1.525 1.0 Comparative example5 *Degree of variability in refraction index to average refractionindex:

Degree of variability was calculated as a larger difference betweeneither the maximum or the minimum of refraction indexes of all samplesand the average refraction index.

TABLE 15 Evaluation result Impact Laminate S-shaped curl strength(kg/cm) strength (g/15 mm) Sample numbers each of Variation VariationLamination Total ⊚, ◯, X Average range Average range processabilityReference ⊚ ⊚ . . . 19, ◯ . . . 2 11.4 10.6-12.0 200 190-210 ◯ example 1Reference ◯ ⊚ . . . 8, ◯ . . . 13 10.7 10.1-11.3 210 200-220 ◯ example 2Reference ⊚ ⊚ . . . 21 13.8 12.9-14.2 300 280-320 ◯ example 3 Reference⊚ ⊚ . . . 19, ◯ . . . 2 10.2 9.9-10.6 200 180-220 ◯ example 4 Reference⊚ ⊚ . . . 19, ◯ . . . 2 11.2 10.8-11.9 200 180-210 ◯ example 5 Reference⊚ ⊚ . . . 17, ◯ . . . 4 10.8 10.2-11.5 230 220-240 ◯ example 6 Reference⊚ ⊚ . . . 13, ◯ . . . 8 10.9 10.4-11.5 230 220-240 ◯ example 7 ReferenceX ⊚ . . . 2, ◯ . . . 6, X . . . 13 11.5 10.2-12.8 200 150-220 XComparative example 1 Reference ◯ ⊚ . . . 3, ◯ . . . 18 11.0 10.1-12.5200 170-250 Δ Comparative example 2 Reference X ◯ . . . 3, X . . . 1810.5  9.5-11.2 210 170-240 Δ Comparative example 3 Reference X ⊚ . . .1, ◯ . . . 8, X . . . 12 11.2 10.3-12.6 230 170-260 X Comparativeexample 4 Reference X ◯ . . . 5, X . . . 16 11.3 10.5-13.2 220 180-280 ΔComparative example 5[Effect of film in Examples]

According to Tables 4 to 8, it is understood that all the film rolls inthe producing method of Examples 1 to 8 had a very small thicknessirregularity over the entire produced roll in the longitudinaldirection, a small variation of physical properties such as boilingwater shrinkage percentage and refraction index in spite of high take-upspeeds of the melted sheet (66 m/min and 75 m/min). Also, it isunderstood that all such film rolls of Examples 1 to 8 providedsatisfactory lamination processability. Furthermore, all film rolls ofExamples 1 through 8 were free of the S-shaped curl phenomenon, and filmthat composed film rolls of Examples 3 through 7 provided good impactstrength (toughness and pinhole resistance) and high laminate strength.In contrast, a film roll of Comparative examples 1 for which glowdischarge was performed without performing streamer corona dischargewhen the melted resin was brought into electrostatically close contactwith the metal roll, as described above, any stretchable unstretchedfilm was unable to be obtained and it was impossible to form film at aspeed similar to that of Example 1.

Also, it is understood from Tables 11 to 15 that all the film rolls ofReference examples 1 to 7 had a very small thickness irregularity overthe entire roll in the longitudinal direction, a small variations ofphysical properties such as boiling water shrinkage percentage,refraction index, etc. were free of the S-shaped curl phenomenon, andprovided good lamination processability. Furthermore, it is understoodthat the films that formed all such film rolls of Examples 1 to 7provided satisfactory impact strength (toughness and pinhole resistance)and high laminate strength. In contrast, film rolls of ReferenceComparative examples 1 through 5 provided large thickness irregularityover the entire rolls in the longitudinal direction or large variationsof physical properties such as boiling water shrinkage percentage andrefraction index, and were subject to the S-shaped curl phenomenon orhad poor lamination processability.

INDUSTRIAL APPLICABILITY

Because the production process of the present invention providesexcellent effect in the aspect of production improvement as describedabove, the production process is able to be suitably used for producingof polyamide based resin film rolls. Also, because the polyamide basedresin film roll obtained by the present invention provide superbprocessing characteristics as described above, the film roll can besuitably used for applications of retort processing for food.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is an explanatory diagram showing the condition in whichelectrodes are disposed in a mobile cooling material and streamer coronadischarge is performed.

DESCRIPTION OF REFERENCE NUMERALS

-   1. Die-   2. Sheet-form melted material-   3. Cooling drum-   4. Unstretched sheet-   5. D.C. high-voltage power supply-   6. Electrode-   7. Streamer corona discharge

1. A process for producing a polyamide based resin film roll taken up ina width of 0.2 m (m is meter) or more, 3.0 m or less, and a length of300 m or more, 30000 m or less, comprising: a step of melt-extruding andcooling wherein polyamide based resin is melt-extruded and cooled in asheet form onto a mobile cooling material surface to obtain anunstretched sheet; a step of biaxial stretching wherein an unstretchedsheet is stretched biaxially in the longitudinal direction and thetransverse direction; and a step of winding up the biaxially stretchedfilm that is biaxially stretched in a form of roll, wherein the step ofmelt-extruding and cooling performs corona discharge in a streamercorona state between an electrode applied with high dc voltage and thepolyamide based resin sheet in the melted state, and imparts sufficientelectric charges that enable the polyamide based resin sheet in themelted state to come in close contact with the mobile cooling materialsurface, and when the polyamide based resin film taken up in a form of aroll has a first sample cutout portion set up within 2 m from thewinding end of film and a final cutout portion within 2 m from thewinding start of film, and at the same time has a sample cutout portionset up in approximately every 100 m from the first sample cutoutportion, the polyamide based resin film taken up in a roll satisfies thefollowing requirements (1) and (2) as well as the following requirements(3); (1) when a maximum boiling water shrinkage percentage which is themaximum value of boiling water shrinkage percentages in all directions,of each sample cut out from each of the cutout portions is measured, anaverage boiling water shrinkage percentage which is average value of themaximum boiling water shrinkage percentages is 2% to 6%, and a degree ofvariability in the maximum boiling water shrinkage percentages of allsamples is within a range of ±2% to ±10% relative to the average boilingwater shrinkage percentage; (2) when a directional difference of boilingwater shrinkage percentage which is an absolute value of the differencebetween a boiling water shrinkage percentage in the direction of +45 tothe longitudinal direction and a boiling water shrinkage percentage inthe direction of −45° to the longitudinal direction of each sample cutout from each of the cutout portion is determined, an averagedirectional difference of boiling water shrinkage percentage which isthe average of the directional differences of boiling water shrinkagepercentage is 1.5% or less, and a degree of variability in thedirectional differences of boiling water shrinkage percentage of allsamples is within a range of ±2% to ±10% relative to the averagedirectional difference of boiling water shrinkage percentage; and (3) adegree of variability in the thickness of a roll wound up over theentire length in the longitudinal direction is within ±2% to ±10%relative to the average thickness.
 2. The production method of polyamidebased resin film roll according to claim 1, wherein when refractionindex in the thick direction of each sample cut out from each of thecutout portions is measured, an average refraction index which is theaverage value of the refraction indexes is 1.500 or more, 1.520 or less,and a degree of variability in the refraction indexes of all samples iswithin a range of ±2% relative to the average refraction index.
 3. Theproduction method of polyamide based resin film roll according to claim1, wherein when refraction index in the thick direction of each samplecut out from each of the cutout portions is measured, an averagerefraction index which is the average of the refraction indexes is 1.500or more, 1.520 or less, and a degree of variability in the refractionindexes of all samples is within a range of ±1% relative to the averagerefraction index.
 4. The production method of polyamide based resin filmroll according to claim 1, wherein the major component of polyamidecomposing the polyamide based resin film is nylon
 6. 5. The productionmethod of polyamide based resin film roll according to claim 1, whereinpolyamide based resin film wound up is formed from a mixture of two ormore different types of mixed substances of polyamide based resin. 6.The production method of polyamide based resin film roll according toclaim 1, wherein the polyamide based resin film wound up is laminatedwith a polyolefin based resin film.
 7. The production method ofpolyamide based resin film roll according to claim 1, wherein apolyamide based resin film wound up is stretched by a tenter stretchingmethod.
 8. The production method of polyamide based resin film rollaccording to claim 1, wherein a polyamide based resin film wound up issequentially biaxially stretched.
 9. The production method of polyamidebased resin film roll according to claim 1, wherein a polyamide basedresin film wound up is a substantially unoriented sheet-like substanceof polyamide based resin, is stretched in at least two stages in thelongitudinal direction to be threefold or more at a higher temperaturethan the glass transition temperature of the polyamide based resin +20°C., and then stretched in the transverse direction to be threefold ormore.
 10. The production method of polyamide based resin film rollaccording to claim 1, wherein a polyamide based resin film taken up isthermally fixed after a final stretching treatment.
 11. The productionmethod of polyamide based resin film roll according to claim 1, whereina polyamide based resin film taken up is thermally fixed after relaxingtreatment.
 12. The production method of polyamide based resin film rollaccording to claim 1, wherein at least one kind selected from lubricant,anti-blocking agent, thermal stabilizer, antioxidant, antistatic agent,light resistant agent and impact modifier is added into the polyamidebased resin film wound up.
 13. The production method of polyamide basedresin film roll according to claim 1, wherein an inorganic particle isadded into the polyamide based resin film wound up.
 14. The productionmethod of polyamide based resin film roll according to claim 13, whereinthe inorganic particle is a silica particle of 0.5-5.0 μm in an averagediameter.
 15. The production method of polyamide based resin film rollaccording to claim 1, wherein a higher fatty acid is added into thepolyamide based resin film wound up.
 16. The production method ofpolyamide based resin film roll according to claim 1, wherein coronadischarge in a stream corona state in the melt-extrusion and coolingstep takes place between a multi-needle-form electrode to which dc highvoltage is applied and the polyamide based resin sheet in a meltedstate.